Remote Tinakula lies 100 km NE of the Solomon Trench at the N end of the Santa Cruz Islands, which are part of the country of the Solomon Islands located 400 km to the W. It has been uninhabited since an eruption with lava flows and ash explosions in 1971 when the small population was evacuated (CSLP 87-71). The nearest communities live on Te Motu (Trevanion) Island (about 30 km S), Nupani (40 km N), and the Reef Islands (60 km E); residents occasionally report noises from explosions at Tinakula. Ashfall from larger explosions has historically reached these islands. The most recent eruptive episode was a large ash explosion and substantial SO₂ plume during 21-26 October 2017; satellite imagery suggested that a flow of some type traveled down the scarp on the W flank. Renewed thermal activity that was recognized in satellite imagery beginning in December 2018 continued intermittently through June 2019 and is covered in this report. Satellite imagery and thermal data are the primary sources of information for this volcano. It is occasionally visited by members of the National Disaster Management Office (NDMO) of the Solomon Islands Government, tourists, and research vessels who are able to capture ground-based information.

Satellite images from December 2018 to February 2019 show thermal anomalies at the summit vent. Excellent ship-based photographs of the island on 24-25 January 2019 provided by a crewmember from the R/V Petrel identify numerous volcanic features and show a steam-and-gas plume at the vent. Satellite images from April and May 2019 show thermal anomalies at both the summit vent and along the W flank scarp suggesting flow activity during that time.

A stream of incandescence on the NW flank of Tinakula in a Sentinel 2 satellite image on 24 October 2017 confirmed that some type of high-temperature flow accompanied the explosions and eruptive activity of 21-25 October 2017 (BGVN 43:02). Satellite imagery during most of 2018 recorded steam plumes drifting in several directions from the summit, but no thermal activity (figure 24). There was no further evidence of activity in satellite visible or thermal data until almost exactly one year later when the MIROVA project recorded two thermal alerts in the third week of October 2018 (figure 25). Satellite images from that week were cloudy and did not confirm any surface activity.

Figure 24. Sentinel-2 satellite imagery of Tinakula provides valuable information about activity at this remote volcano in the South Pacific. A large explosion with ash plumes and flows occurred during 21-26 October 2017. Top left: a strong E-W linear thermal anomaly suggesting a flow event from the summit was evident on the NW flank on 24 October 2017. Top right: a small steam plume rose from the summit vent on a cloudless 11 February 2018. Bottom left: a dense steam plume drifted SE from the summit vent on 4 September 2018. Bottom right: clouds and dense steam obscure the summit on 24 October 2018, about the same time that MIROVA reported a thermal anomaly. Top left image uses bands 12, 11, 8A, others use 12, 4, 2. Courtesy of Sentinel Hub Playground.

Figure 25. The MIROVA project recorded the first thermal anomaly in a year from Tinakula during the third week of October 2018. Courtesy of MIROVA.

The first satellite imagery confirming renewed thermal activity appeared on 8 December 2018, around the same time as a small MIROVA anomaly. After that, several images during January and February 2019 confirmed moderately strong thermal activity at the summit (figure 26). Whether the anomalies were the result of active lava effusion or strong incandescent gases from the summit vent is uncertain.

Figure 26. Thermal anomalies at the summit vent of Tinakula were recorded six times between early December 2018 and early February 2019 with Sentinel-2 satellite images. Top row: 8 December 2018 and 2 January 2019. Middle row: 12 (anomaly is just below date) and 27 January 2019. Bottom row: 1 and 6 February 2019. All images are bands 12, 4, 2. Courtesy of Sentinel Hub Playground.

Visual confirmation of activity at Tinakula is rare, but the research vessel R/V Petrel sailed past the volcano on 24 and 25 January 2019 and a crewmember provided detailed images of the W flank and vent area. The summit vent is located at the top of a W facing scarp, and steam is frequently observed rising from the vent (figures 27). Recent flows and volcaniclastic deposits were visible in the ravine on the W flank (figures 28 and 29). Fresh-looking lava was also visible near the summit vent on top of older deposits (figure 30). Eroded volcaniclastic deposits near the base of the scarp on the W flank were visible on top of older veined and layered volcanic rocks (figure 31). Crewmembers on the vessel R/V Petrel could clearly see an incandescent glow from the summit crater at night (figure 32).

Figure 27. A view from the SW of the W flank of Tinakula on 24-25 January 2019. The summit vent is at the top of a W facing scarp, the steam plume drifted E. Used with permission from Paul G Allen's Vulcan Inc.

Figure 28. The W flank of Tinakula as seen from the W on 24-25 January 2019. The steam plume drifted E. Recent flows and volcaniclastic deposits appeared dark in the steep ravine on the W face (left side). Used with permission from Paul G Allen's Vulcan Inc.

Figure 29. Steam and gas rose from the summit vent at Tinakula on 24-25 January 2019. Recent lava deposits are visible in front of the plume and in the ravine on the left (the W flank). Used with permission from Paul G Allen's Vulcan Inc.

Figure 30. The edge of the summit vent of Tinakula on 24-25 January 2019 had recent lava on older deposits; steam and gas is rising from the vent in the background. Used with permission from Paul G Allen's Vulcan Inc.

Figure 31. The W flank of Tinakula on 24-25 January 2019. Eroded volcaniclastic deposits overlie older veined and layered volcanic rocks. Used with permission from Paul G Allen's Vulcan Inc.

Figure 32. Incandescence was clearly visible from the summit vent at Tinakula on 24-25 January 2019. Used with permission from Paul G Allen's Vulcan Inc.

During April and May 2019, both the MIROVA project and MODVOLC measured a number of thermal anomalies (figure 33) using MODIS satellite data. MODVOLC alerts were issued on 4 and 20 April, and 11, 18, and 27 May. Sentinel-2 satellite images during the period confirmed that a flow on the W flank was a likely source of the thermal energy in addition to the summit vent (figure 34). Thermal anomalies appeared again at the end of June in MIROVA data, but no satellite images showed anomalies at that time.

Figure 33. The number and intensity of MIROVA thermal anomalies increased at Tinakula during April and May 2019. After a short pause, they returned at the end of June. Courtesy of MIROVA.

Figure 34. Sentinel-2 satellite images captured thermal anomalies at the summit and on the W flank of Tinakula during April and May 2019 suggesting the presence of an incandescent flow down the W scarp. Top row: 7 and 22 April 2019 (bands 12, 8, 4). Bottom row: 27 April and 12 May 2019 (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

Geologic Background. The small 3.5-km-wide island of Tinakula is the exposed summit of a massive stratovolcano at the NW end of the Santa Cruz islands. Similar to Stromboli, it has a breached summit crater that extends from the summit to below sea level. Landslides enlarged this scarp in 1965, creating an embayment on the NW coast. The satellitic cone of Mendana is located on the SE side. The dominantly andesitic volcano has frequently been observed in eruption since the era of Spanish exploration began in 1595. In about 1840, an explosive eruption apparently produced pyroclastic flows that swept all sides of the island, killing its inhabitants. Frequent historical eruptions have originated from a cone constructed within the large breached crater. These have left the upper flanks and the steep apron of lava flows and volcaniclastic debris within the breach unvegetated.

Information Contacts: MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Vulcan Inc. (URL: https://www.vulcan.com/), additional details about the R/V Petrel (URL: https://www.paulallen.com/).

Short pulses of intermittent eruptive activity have characterized Piton de la Fournaise, the large basaltic shield volcano on La Réunion Island in the western Indian Ocean, for several thousand years. For the last 20 years, frequent effusive basaltic eruptions have occurred on average twice per year. The activity is characterized by lava fountains and lava flows, and occasional explosive eruptions that shower blocks over the summit area and produce ash plumes. Almost all of the recent activity has occurred within the Enclos Fouqué caldera, although past eruptions in 1977, 1986, and 1998 have occurred at vents outside of the caldera. Four separate eruptive episodes were reported during 2018; from 3-4 April, 27 April-1 June, 13 July, and 15 September-1 November (BGVN 43:12, 43:09). Two episodes from 2019 during February-March and June are covered in this report, with information provided primarily by the Observatoire Volcanologique du Piton de la Fournaise (OVPF) as well as satellite instruments.

Piton de la Fournaise experienced two eruptions during November 2018-June 2019. The first lasted from 18 February to 10 March 2019, and the second episode was 11-13 June. The episode in February-March started consisted of multiple fissures opening on the E flank of the Dolomieu crater on 18 February with lava flows that traveled several hundred meters. After a brief pause, one new fissure opened nearby on 19 February and produced up to 3 million m³ of lava in a little over four days. Although the flow rate then declined, the eruption continued until 10 March. During the last three days, 7-10 March, two new fissures opened nearby and produced large volumes of lava, bringing the total eruptive volume to about 14.5 million m³. After little activity during April and May, a small eruption occurred on the SSE outer slope of Dolomieu crater that lasted for about 48 hours on 11-13 June; multiple small flows traveled about 1,000 m down the steep flank before ceasing. The MIROVA thermal anomaly graph of log radiative power clearly showed the abruptness of the beginning and ends of the last three eruptive episodes at Piton de la Fournaise from August 2018 through June 2019 (figure 165).

Figure 165. The MIROVA graph of thermal energy from Piton de la Fournaise from 30 July 2018 through June 2019 shows the last three eruptive episodes at the volcano. From 15 September through 1 November 2018 fissures and flows were active on the SW flank of Dolomieu crater near Rivals crater (BGVN 43:12). Fissures opened on the E flank of the crater on 18 February 2019, and after a brief pause resumed on 19 February at the foot of Piton Madoré. Lava flows remained active until 10 March 2019. A short episode of lava effusion occurred on 11-12 June 2019 on the SSE outer slope of Dolomieu crater. Courtesy of MIROVA.

Activity during November 2018-March 2019. Following the end of the 15 September-1 November 2018 eruption, seismic activity immediately below the summit remained low (with only 20 shallow and two deep earthquakes during November). The inflationary signal recorded since the beginning of September stopped, and the OVPF deformation networks did not record any significant deformation. There were 35 shallow earthquakes (0-2 km depth) below the summit crater during December, and one deep earthquake. Only 12 shallow earthquakes and one deep earthquake (greater than 2 km below the surface) were reported in January.

OVPF reported an increase in CO₂ concentrations beginning in December 2018, and noted the beginning of inflation on 13 February 2019. A seismic swarm of 379 earthquakes accompanied by minor but rapid deformation (less than 1 cm) was reported on 16 February 2019. A new seismic swarm of 208 earthquakes began early on 18 February with a much larger ground deformation (10 cm of elongation of the summit zone). A volcanic tremor indicative of the arrival of magma near the surface began at 0948 that morning. Webcams indicated that eruptive fissures had opened in the NE part of the Enclos Fouqué caldera. The onset of the eruption was marked by a sudden drop in CO₂ flux which then stabilized. The eruptive sites were confirmed visually around 1130. Three fissures with actively flowing lava opened on the E flank of Dolomieu Crater; the fountains of lava were less than 30 m high. The front of the longest flow had reached 1,900 m elevation after one hour. The eruption lasted a little over 12 hours and was over by 2200 that evening; it covered about 150-200 m of the hiking trail to the summit.

Seismicity remained high after the event ended, and at 1500 on 19 February 2019 another seismic swarm of 511 deep earthquakes located under the E flank at about 2.5 km depth occurred. It was not accompanied by a significant amount of deformation. At 1710 tremor signals appeared on the observatory seismographs and the first gas plumes and lava ejection were observed at 1750 and 1912, respectively. During an overflight the next day (20 February), OVPF team members observed the new eruptive site at an elevation of 1,800 m at the foot of Piton Madoré. One fissure and one fountain were active at 0620 on 20 February and the flow front was at 1,300 m elevation (figure 166). During the night of 20-21 February the flow front crossed over the "Grandes Pentes" area in the eastern half of the Enclos Fouque (figure 167).

Figure 166. The eruption which began on 19 February 2019 on the E flank of Dolomieu crater at Piton de la Fournaise produced a lava fountain and flow which traveled down at least 500 m of elevation by the next morning when this photo was taken at 0620 local time. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du mercredi 20 février 2019 à 11h00, Heure locale).

Figure 167. The active fissure at Piton de la Fournaise was producing lava fountains and an active flow during the evening of 20 February 2019. Overnight the flow crossed over the "Grandes Pentes" area of the caldera. Photo courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du jeudi 21 février 2019 à 14H00, Heure locale).

OVPF reported on 22 February 2019 that 22 shallow earthquakes had been reported since the eruption began on 19 February. Surface flow rates estimated from satellite data, via the HOTVOLC system (OPGC - University of Auvergne), were between 2.5 and 15 m³/s. The quantity of lava emitted between 19 and 22 February was between 1 and 3 million m³. OVPF observed the growth of an eruptive cone that was filled with a small lava lake producing ejecta during a morning overflight on 22 February. A channelized flow moved downstream from the cone and split into two lobes about 1 km from (and 200 m below) the cone (figure 168). The split in the flow occurred near the Guyanin crater. The N flowing lobe, about 50 m wide, had an actively flowing front located at 1,320 m elevation; the incandescent flow was travelling over a recent flow (likely from the previous night). The S-flowing lobe spread to 200 m wide and split into two tongues 300 m SE of Guyanin crater.

Figure 168. During an overflight on the morning of 22 February 2019 scientists from OVPF observed a growing spatter cone with a small lava lake at Piton de la Fournaise. A channelized flow moved downstream from the fissure and split into two flows. Photo courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du vendredi 22 février 2019 à 13h30, Heure locale).

Incandescent ejecta from the cone was captured in a webcam image overnight on 22-23 February 2019 (figure 169). The rate of advance of the flow slowed significantly by 24 February, but the intensity of the eruptive tremor remained relatively constant. Mapping of the lava flow on 28 February carried out by the OI2 platform (OPGC - University Clermont Auvergne) from satellite data confirmed the slow progress of the flow after 24 February (300 m in 5 days) (figure 170). The flow front was located at 1,200 m elevation, and only the N arm was active; the lava had traveled about 2.2 km from the vent by 28 February.

Figure 169. Incandescent ejecta from the eruptive cone at Piton de la Fournaise was captured in the webcam in the early hours of 23 February 2019. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du samedi 23 février 2019 à 13h30, Heure locale).

Figure 170. Contours of the lava flows at Piton de la Fournaise from 18-28 February 2019 were determined from satellite data by the OI2 platform (Université Clermont Auvergne), dated 18 (red) and 19 (blue) February (top image); 20 (green), 21 (red), 22 (blue), 27 (turquoise), and 28 (pink) February (bottom image). Courtesy of and copyright by OVPF/IPGP. Top: Bulletin d'activité du vendredi 22 février 2019 à 13h30 (Heure locale); bottom: Bulletin d'activité du jeudi 28 février 2019 à 16h30 (Heure locale).

Between 28 February and 1 March 2019 a third lobe of lava appeared flowing NE from the vent on the N side of the new flow area; it split into two lobes sometime on 1 March. Very little new lava was recorded on the other lobes. By 4 March the flow rate estimated by satellite data was about 7.5 m³/s. During a site visit on the morning of 5 March OVPF scientists sampled the N lobe of the flow and bombs and tephra near the cone, and acquired infrared and visible images. They noted the continued growth of the cone which still had an open vent at the summit and a base 100 m in diameter. It was 25 m high with a 50-m-wide eruptive vent at the top (figure 171). High-temperature gas emissions and strong Strombolian activity issued from the vent. Steam emissions were present around the base of the cone, suggesting the presence of lava tunnels. A single lobe of lava flowed N from the cone.

Figure 171. The eruptive cone at Piton de la Fournaise on 5 March 2019 had a 100-m-diameter base, 25 m of vertical height, and 50-m-wide vent at the summit. Courtesy of and copyright by OVPF/IPGP, (Bulletin d'activité du mardi 5 mars 2019 à 17h30, Heure locale).

A new fissure that opened about 150 m from the main vent on the NW flank of Piton Madoré was first observed on the morning of 6 March (figure 172); OVPF concluded that it had opened late on 5 March. A small cone was forming and a new flow traveled N from the main eruptive site. At least six new emission points were noted the following morning (7 March) around the Piton Madoré. Poor weather prevented confirmation by aerial reconnaissance that day, but in a site visit on 8 March OVPF scientists determined that the new fissure from 5 March remained active; a small cone about 10 m high had two flow lobes on the W and N sides (figure 173). A fissure that opened on 7 March was located 300 m S of the 19 February vent and oriented E-W. It was very active on the morning of 8 March with two 50-m-high lava fountains (figure 174). Samples collected by OVPF indicated that the vents of 5 and 7 March produced lava of different compositions.

Figure 172. A new fissure that opened about 150 m from the main vent on the NW flank of Piton Madoré at Piton de la Fournaise was first observed on the morning of 6 March 2019; OVPF concluded that it had opened late on 5 March. A small cone was forming on the flank of an old one and a new flow traveled N from the main eruptive site. Courtesy of OVPF/IPGP, copyright by Helicopter Coral (Bulletin d'activité du jeudi 7 mars 2019 à 15h00 Heure locale).

Figure 173. The 5 March 2019 fissure at Piton de la Fournaise on the NW flank of Piton Madoré still had two active flow lobes emerging from it and heading N and W on 8 March 2019. Courtesy of and copyright by OVPF/IPGP (Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, March 2019).

Figure 174. A fissure that opened on 7 March 2019 at Piton de la Fournaise was located 300 m S of the 19 February vent and oriented E-W. It was very active on the morning of 8 March 2019 with two 50-m-high lava fountains. Courtesy of and copyright by OVPF/IPGP (Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, March 2019).

There was a strong increase in the eruptive tremor intensity on 7 March, related to the opening of the two new fissures on 5 and 7 March (figure 175). As a result, the surface flow estimates made from satellite data increased significantly to high values greater than 50 m³/s, with the average values on 7-8 March of around 20-25 m³/s. The increased flow rates resulted in the flows traveling much greater distances. By the morning of 9 March the active flow had reached 650-700 m above sea level. The flow front had traveled about 1 km in 24 hours. Strong seismicity had been increasing under the summit zone for the previous 48 hours. After a phase of very strong surface activity observed overnight on 9-10 March that included lava fountains 50-100 m high (figure 176), surface activity ceased around 0630 on 10 March, and seismic activity decreased significantly. OVPF noted that sudden increases in seismicity and flow rates near the end of an eruption have occurred at about half of the eruptions at Piton de la Fournaise in recent years. Lava volumes emitted on the surface between 18 February and 10 March 2019 were estimated at about 14.5 million m³ (figure 177).

Figure 175. An infrared view of the eruptive site on the E flank of Dolomieu crater at Piton de la Fournaise on 8 March 2019 clearly showed the original fissure from 19 February (bottom right of center), the fissure on Piton Madore that opened on 5 March (right) and the fissures that opened on 7 March (upper, right of center). The combined activity produced significant thermal and seismic activity at the volcano. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du vendredi 8 mars 2019 à 17h00, Heure locale).

Figure 176. Lava fountains 50-100 m high were the result of very strong surface activity observed overnight on 9-10 March 2019 at Piton de la Fournaise. Surface activity ceased around 0630 on 10 March, and seismic activity decreased significantly. Photo taken on 9 March 2019 around midnight from the RN2. Courtesy of OVPF/IPGP, copyright by A. Finizola LGSR/IPGP (Bulletin d'activité du dimanche 10 mars 2019 à 19h30 Heure locale).

Figure 177. A sudden increase in the flow rate at the end of the 18 February-10 March 2019 eruption at Piton de la Fournaise was recorded by researchers at the Université Clermont Auvergne. OVPF noted this was typical of about half of the eruptions at Piton de la Fournaise. Courtesy of OVPF/IPGP, copyright by HOTVOLC, Université Clermont Auvergne (OVPF Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, March 2019).

Significant SO₂ plumes were captured by the TROPOMI instrument on the Sentinel 5-P satellite throughout the 18 February-10 March eruption (figure 178). After the surface eruption ceased, shallow seismicity continued at a lower rate of about 12 earthquakes per day. The end of the eruption (7-10 March) was accompanied by a marked deflation, interpreted by OVPF as the rapid emptying of the magma reservoir. Following the end of the eruption, inflation resumed for the rest of March but then ceased. Seismicity continued at a lower level during April with an average of six shallow earthquakes per day.

Figure 178. Multiple days of high DU value SO2 plumes were recorded by the TROPOMI instrument on the Sentinel 5-P satellite during the 18 February-10 March 2019 eruption at Piton de la Fournaise. Top row: during 18, 21, and 22 February SO2 plumes drifted SE. Middle row: during 23, 24, and 25 February the wind direction changed from SE through S to SW and left a curling trail of SO2. Bottom row: 5, 7, and 8 March showed an increase in SO2 emissions that corresponded with increased seismicity and lava flow output before the eruption ceased.

Activity during May-June 2019. OVPF reported slight inflation near the summit beginning in early May, and an increase in CO₂ concentration in the soil near Plaine des Cafres and Plaine des Palmistes. Strong shallow seismicity reappeared on 27 May 2019 and recurred on 30 and 31 May. Two small seismic swarms were measured on 31 May in the early morning. A new seismic swarm beginning at 0603 on 11 June accompanied by rapid deformation suggested a new eruption was imminent. A tremor near the summit area was first noted at 0635 local time; the webcams indicated a plume of gas, but poor visibility prevented evidence of fresh lava. Around 0930 that morning OVPF confirmed that five fissures had opened on the outer SSE slope of Dolomieu crater at elevations ranging from 2480 to 2025 m (figure 179). The flow fronts were not visible due to weather. Lava fountains under 30 m in height and lava flows were present in the three lowest fissures. The flows traveled rapidly down the steep flank of the crater (figure 180).

Figure 179. Around 0930 on the morning of 11 June 2019 OVPF confirmed that five fissures had opened on the outer SSE slope of Dolomieu crater at Piton de la Fournaise at elevations ranging from 2480 to 2025 m. Courtesy of and copyright by OVPF-IPGP and Imazpress (Bulletin d'activité du mardi 11 juin 2019 à 11h00).

Figure 180. Thermal imaging of the 11-12 June 2019 eruptive site at Piton de la Fournaise showed multiple streams of lava traveling rapidly down the steep flank from several fissures on 11 June 2019. Courtesy of and copyright by OVPF-IPGP (Bulletin d'activité du mardi 11 juin 2019 à 11h00).

The intensity of the eruptive tremor decreased throughout the day, and by 1530 only the lowest elevation fissure was still active (figure 181). The next afternoon (12 June) images in the OVPF webcam located in Piton des Cascades indicated the flow front was at about 1,200-1,300 m elevation. Seismographs indicated that the eruption stopped around 1200 on 13 June. Poor weather obscured visibility of the flow activity. Seismic activity decreased following the eruption, but appeared to increase again beginning on 21 June, with 10 events detected on 30 June. SO₂ plumes were recorded in satellite data on 11 and 12 June 2019.

Figure 181. The intensity of the eruptive activity at Piton de la Fournaise on 11 June 2019 decreased throughout the day, and by 1530 only the lowest elevation fissure was still active. Courtesy of and copyright by OVPF-IPGP (Bulletin d'activité du mardi 11 juin 2019 à 17h45 Heure locale).

Geologic Background. The massive Piton de la Fournaise basaltic shield volcano on the French island of Réunion in the western Indian Ocean is one of the world's most active volcanoes. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three calderas formed at about 250,000, 65,000, and less than 5000 years ago by progressive eastward slumping of the volcano. Numerous pyroclastic cones dot the floor of the calderas and their outer flanks. Most historical eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest caldera, which is 8 km wide and breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures on the outer flanks of the caldera. The Piton de la Fournaise Volcano Observatory, one of several operated by the Institut de Physique du Globe de Paris, monitors this very active volcano.

Information Contacts: Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, 14 route nationale 3, 27 ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://www.ipgp.fr/fr); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

The ongoing eruption at Semeru has been characterized by numerous ash explosions and thermal anomalies, but activity apparently diminished in 2018 (BGVN 43:01 and 43:09); this decreased activity continued through at least February 2019. The current report summarizes activity from 24 August 2018 to 28 February 2019.

The Indonesian volcano monitoring agency, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), reported ongoing daily seismicity, dominated by explosion earthquakes and emission-related events from late November through February (figure 35). Ash plumes resulting in aviation advisories by the Darwin Volcanic Ash Advisory Centre (VAAC) were reported on 4, 6-7, and 19 September, and 12 October 2018. The next significant ash plume reported by the VAAC wasn't until 24 February 2019 (table 23).

Figure 35. Seismicity recorded at Semeru during 28 November 2018-26 February 2019. Plot shows explosion earthquakes ('Letusan'), emission-related events ('Hembusan'), felt earthquakes ('Gempa Terasa'), local tectonic events ('Tektonic Lokal'), and distant tectonic events ('Tektonic Jauh'). Courtesy of PVMBG and MAGMA Indonesia.

Table 23. Summary of ash plumes at Semeru during 25 August 2018 through February 2019. The summit is at 3,657 m elevation. Data courtesy of Darwin VAAC.

Thermal anomalies using MODIS satellite instruments processed by the MODVOLC algorithm were only recorded on 26, 28, and 30 August 2018, and 22 and 31 October 2018. The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected numerous hotspots within 5 km of the volcano during August and early September, with a significant decrease in frequency through October (figure 36); only a few scattered hotspots were recorded from November 2018 through February 2019.

Figure 36. MIROVA plot of thermal anomalies (Log Radiative Power) at Semeru during July 2018-February 2019. Courtesy of MIROVA.

Geologic Background. Semeru, the highest volcano on Java, and one of its most active, lies at the southern end of a volcanic massif extending north to the Tengger caldera. The steep-sided volcano, also referred to as Mahameru (Great Mountain), rises above coastal plains to the south. Gunung Semeru was constructed south of the overlapping Ajek-ajek and Jambangan calderas. A line of lake-filled maars was constructed along a N-S trend cutting through the summit, and cinder cones and lava domes occupy the eastern and NE flanks. Summit topography is complicated by the shifting of craters from NW to SE. Frequent 19th and 20th century eruptions were dominated by small-to-moderate explosions from the summit crater, with occasional lava flows and larger explosive eruptions accompanied by pyroclastic flows that have reached the lower flanks of the volcano.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

Heard Island, in the Southern Indian Ocean, includes the large Big Ben stratovolcano and the smaller, apparently inactive, Mt. Dixon. Because of the island's remoteness, satellites are the primary monitoring tool. Big Ben has been active intermittently since 1910, and was active during October 2017-September 2018 (BGVN 43:10). Activity continued during October 2018-March 2019.

Satellite photos using Sentinel Hub showed hotspots every month between October 2018 and March 2019. Because the area was frequently covered by a heavy cloud layer, most of the hotspot signals were partially obscured. Though thermal anomalies are usually seen at summit vents, on 18 October 2018 an anomaly was present about 300 m down the E flank. Similarly, on 1 January 2019, a weak anomaly beginning about 200 m down the NW flank was about 300 m long (figure 40).

The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected three hotspots, two in October and one in early November 2018, all of low radiative power. There were no MODVOLC alert pixels during this period.

Figure 40. Sentinel-2 L1C image of Heard Island's Big Ben volcano on 1 January 2019 one summit hotspot and an elongated thermal anomaly to the NW. Scale bar (bottom right) is 200 m. The photo was taken in atmospheric penetration view (bands 12, 11, and 8A), courtesy of Sentinel Hub Playground.

Geologic Background. Heard Island on the Kerguelen Plateau in the southern Indian Ocean consists primarily of the emergent portion of two volcanic structures. The large glacier-covered composite basaltic-to-trachytic cone of Big Ben comprises most of the island, and the smaller Mt. Dixon volcano lies at the NW tip of the island across a narrow isthmus. Little is known about the structure of Big Ben volcano because of its extensive ice cover. The historically active Mawson Peak forms the island's 2745-m high point and lies within a 5-6 km wide caldera breached to the SW side of Big Ben. Small satellitic scoria cones are mostly located on the northern coast. Several subglacial eruptions have been reported in historical time at this isolated volcano, but observations are infrequent and additional activity may have occurred.

Information Contacts: Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

The eruption at Dukono that began in 1933 has showered the area with ash from frequent explosions (BGVN 43:04, 43:12). The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as the Center for Volcanology and Geological Hazard Mitigation (CVGHM), is responsible for monitoring this volcano.

This long-term pattern of intermittent ash explosions continued during October 2018-March 2019, with ash plumes rising to between 1.5 and 2.7 km altitude, or about 300-1,500 m above the summit (table 19). Although meteorological clouds often obscured views, satellite imagery captured typical ash plumes on 28 September 2018 (figure 10) and 5 February 2019 (figure 11). Instruments aboard NASA satellites (TROPOMI and OMPS) detected high levels of sulfur dioxide near or directly above the volcano on multiple days during January-March 2019. The Alert Level remained at 2 (on a scale of 1-4), and visitors were warned to remain outside of the 2-km exclusion zone.

Table 19. Monthly summary of reported ash plumes from Dukono for October 2018-March 2019. The direction of drift for the ash plume through each month was highly variable. Data courtesy of the Darwin VAAC and PVMBG.

Figure 10. Satellite image from Sentinel-2 (LC1 natural color) of an ash plume at Dukono on 28 September 2018 with the plume blowing towards the NE. Courtesy of Sentinel Hub Playground.

Figure 11. Satellite image from Sentinel-2 (LC1 natural color) of an ash plume at Dukono on 5 February 2019, with the plume blowing SW. Courtesy of Sentinel Hub Playground.

Geologic Background. Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia's most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the north-flank cone of Gunung Mamuya. This complex volcano presents a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also been active during historical time.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Intermittent small phreatic explosions from the acid lake of Rincón de la Vieja's active crater has most recently occurred since 2011 (BGVN 42:08, 43:03, and 43:09). This activity continued through at least February 2019. The volcano is monitored by the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), and the information below comes from its weekly bulletins between 18 August 2018 and 28 February 2019. Weather conditions often prevented webcam views and estimates of plume heights. The volcano was in Activity Level 3 throughout the reporting period (volcano erupting, steady state).

According to OVSICORI-UNA, two distinct, 2-minute-long explosions occurred on 31 August 2018 beginning at 0434 and 1305. Several hours after the eruption tremor became continuous but low-frequency long-period (LP) earthquakes ceased. OVSICORI-UNA reported a gas emission late on 7 September. An unconfirmed small phreatic explosion occurred on 11 September at 0634, and another on 17 September at 1014. The seismic record showed continuous background tremor and very sporadic LP earthquakes.

Intermittent background tremor was recorded during the first half of October, along with a few emissions and phreatic explosions. Deformation measurements during October showed a contraction between the N and S of the volcano, with subsidence. On 17 October there was another phreatic explosion, and thereafter tremor disappeared and seismicity decreased. On 23 and 27 October seismic stations signaled additional possible phreatic explosions.

OVSICORI-UNA reported that a series of explosions began at 1945 on 4 November and consisted of at least three 2-minute-long episodes. The next day at 1511 a plume of water vapor and diffuse gas, recorded by a webcam and visible to residents to the N, rose about 100 m above the crater rim and drifted W. On 9 November a 2-minute-long explosion began at 1703. Another explosion on 27 November at 0237 produced a plume of water vapor and gas that rose 600 m above the crater rim and drifted SW. A short 1-minute explosion began at 1054 on 3 December.

Based on OVSICORI-UNA weekly bulletins, activity remained stable in January 2019 with small-amplitude phreatic explosions on 11, 12, and 14 January. More energetic phreatomagmatic explosions on 17 and 20 January produced lahars. Several small-amplitude explosions were detected at the end of the month. During January, a few LPs, no VTs, and intermittent tremor were recorded.

OVSICORI-UNA reported that two small-scale explosions occurred on 1 February, along with possible events at 1906 and 1950 on 5 February and at 0120 on 6 February. An event at 0000 on 6 February was also recorded; the report noted that poor weather conditions prevented visual observations of the crater. On 16 and 17 February strong degassing was observed. No LPs were recorded, but two significant VTs were detected on 17 and 22 February near or under the crater.

Geologic Background. Rincón de la Vieja, the largest volcano in NW Costa Rica, is a remote volcanic complex in the Guanacaste Range. The volcano consists of an elongated, arcuate NW-SE-trending ridge that was constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the "Colossus of Guanacaste," it has an estimated volume of 130 km3 and contains at least nine major eruptive centers. Activity has migrated to the SE, where the youngest-looking craters are located. The twin cone of 1916-m-high Santa María volcano, the highest peak of the complex, is located at the eastern end of a smaller, 5-km-wide caldera and has a 500-m-wide crater. A plinian eruption producing the 0.25 km3 Río Blanca tephra about 3500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous historical eruptions possibly dating back to the 16th century, have been from the prominent active crater containing a 500-m-wide acid lake located ENE of Von Seebach crater.

Information Contacts: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/).

This report summarizes activity at Turrialba during September 2018-February 2019. During this period there was similar activity as described earlier in 2018 (BGVN 43:09), with occasional ash explosions and numerous, sometimes continuous, periods of gas-and-ash emissions (table 8). Data were provided by the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA).

Table 8. Ash emissions at Turrialba, September 2018-February 2019. Cloudy weather sometimes obscured observations. Maximum plume height is above the crater rim. Information courtesy of OVSICORI-UNA.

According to OVSICORI-UNA's annual summary for 2018, a slow decline in activity occurred after the volcano reached its highest emission rate during 2016. Activity during 2018 was consistent with an open system, generating frequent passive ash emissions. The volcano emitted ash on 58% of the days during the year. Some explosions were large enough to eject ballistics more than 400 m around the crater. Typical activity can be seen in a photo from 11 September 2018 (figure 50) and satellite imagery on 7 November 2018 (figure 51).

Figure 50. Photo of an ash explosion at Turrialba taken on 11 September 2018. Courtesy of Red Sismologica Nacional (RSN: UCR-ICE), Universidad de Costa Rica.

Figure 51. Sentinel-2 satellite image of an ash emission from Turrialba on 7 November 2018, taken in natural color (gamma adjusted). Courtesy of Sentinel Hub Playground.

During January into early February 2019, passive ash emissions continued irregularly and with less intensity and duration. Emissions sometimes lacked ash. In their report of 4 February 2019, OVSICORI-UNA indicated that passive ash emissions were weak and slow. For the rest of February, they characterized ash emissions as frequent, but of low intensity.

Seismic activity. On 1 November 2018 OVSICORI-UNA reported that seismicity remained high, and involved low-amplitude banded volcanic tremor along with long-period (LP) and volcano-tectonic (VT) earthquakes. In late January-early February 2019, OVSICORI-UNA reported that seismicity remained relatively stable, although a small increase was associated with the hydrothermal system. VT earthquakes were absent, and tremors had decreased in both energy and duration. The number of low-frequency LP volcanic earthquakes remained stable, although they had decreasing amplitudes. No explosions were documented, and emissions were weak and had short durations and very dilute ash content.

Thermal anomalies. No thermal anomalies were recorded during the reporting period using MODIS satellite instruments processed by MODVOLC algorithm. The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected five scattered hotspots during September-October 2018, none during November-December 2018, and two during January-February 2019. All were within 2 km of the volcano and of low radiative power.

Gas measurements. Significant sulfur dioxide levels near the volcano were recorded by NASA's satellite-borne ozone instruments only on 29 September 2018 (both NPP/OMPS and Aura/OMI instruments) and on 11 February 2019 (Sentinel 5P/TROPOMI instrument). OVSICORI-UNA's gas measuring instruments were compromised in September 2018 through January 2019 due to vandalism. In early February, however, they detected hydrogen sulfide for the first time since 2016.

Geologic Background. Turrialba, the easternmost of Costa Rica's Holocene volcanoes, is a large vegetated basaltic-to-dacitic stratovolcano located across a broad saddle NE of Irazú volcano overlooking the city of Cartago. The massive edifice covers an area of 500 km2. Three well-defined craters occur at the upper SW end of a broad 800 x 2200 m summit depression that is breached to the NE. Most activity originated from the summit vent complex, but two pyroclastic cones are located on the SW flank. Five major explosive eruptions have occurred during the past 3500 years. A series of explosive eruptions during the 19th century were sometimes accompanied by pyroclastic flows. Fumarolic activity continues at the central and SW summit craters.

Information Contacts: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/); Red Sismologica Nacional (RSN) a collaboration between a) the Sección de Sismología, Vulcanología y Exploración Geofísica de la Escuela Centroamericana de Geología de la Universidad de Costa Rica (UCR), and b) the Área de Amenazas y Auscultación Sismológica y Volcánica del Instituto Costarricense de Electricidad (ICE), Costa Rica (URL: https://rsn.ucr.ac.cr/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://hotspot.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Costa Rica Star (URL: https://news.co.cr); The Tico Times (URL: https://ticotimes.net).

San Cristóbal has produced occasional weak explosions since 1999, with intermittent gas-and-ash emissions. The only reported explosion during the first half of 2018 was on 22 April, the first since November 2017 (BGVN 43:03). The current report covers activity between 1 August 2018 and 1 May 2019. The volcano is monitored by the Instituto Nicaragüense de Estudios Territoriales (INETER).

According to INETER, a series of explosions occurred on 9 January 2019 that lasted several hours. INETER stated that one explosion occurred at 1643; the Washington VAAC's first advisory stated that an explosion occurred at 1145 (local time). The weak explosions, which occurred after a period of heightened seismic activity, generated an ash plume that reached 200 m above the edge of the crater and drifted W. The Washington VAAC reported volcanic ash plumes on 10-11 January extending about 92 km SW, and on 24-25 January extending about 185 km WSW. A low-energy explosion was detected by the seismic network at 1550 on 4 March 2019. The event produced a gas-and-ash plume that rose 400 m above the crater rim and drifted SW.

Monitoring data reported by INETER (table 6) showed elevated levels of seismicity during October 2018 through January 2019. Sulfur dioxide was also measured at higher levels in January 2019.

Table 6. Monthly sulfur dioxide measurements and seismicity reported at San Cristóbal during August 2018-March 2019. "Most" indicates that type of seismicity was dominant that month. Data courtesy of INETER.

Geologic Background. The San Cristóbal volcanic complex, consisting of five principal volcanic edifices, forms the NW end of the Marrabios Range. The symmetrical 1745-m-high youngest cone, named San Cristóbal (also known as El Viejo), is Nicaragua's highest volcano and is capped by a 500 x 600 m wide crater. El Chonco, with several flank lava domes, is located 4 km W of San Cristóbal; it and the eroded Moyotepe volcano, 4 km NE of San Cristóbal, are of Pleistocene age. Volcán Casita, containing an elongated summit crater, lies immediately east of San Cristóbal and was the site of a catastrophic landslide and lahar in 1998. The Plio-Pleistocene La Pelona caldera is located at the eastern end of the complex. Historical eruptions from San Cristóbal, consisting of small-to-moderate explosive activity, have been reported since the 16th century. Some other 16th-century eruptions attributed to Casita volcano are uncertain and may pertain to other Marrabios Range volcanoes.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://webserver2.ineter.gob.ni/vol/dep-vol.html); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html).

The remote Semisopochnoi comprises the uninhabited volcanic island of the same name, ~20 km in diameter, in the Rat Islands group of the western Aleutians (figure 1). Plumes had been reported several times in the 18th and 19th centuries, and most recently observed in April 1987 from Sugarloaf Peak (SEAN 12:04). The volcano is dominated by an 8-km diameter caldera that contains a small lake (Fenner Lake) and a number of post-caldera cones and craters. Monitoring is done by the Alaska Volcano Observatory (AVO) using an on-island seismic network along with satellite observations and lightning sensors. An infrasound array on Adak Island, about 200 km E, may detect explosive emissions with a 13 minute delay if atmospheric conditions permit.

On 16 September 2018 increased seismicity was detected at 0831, prompting AVO to raise the Aviation Color Code (ACC) to Yellow and Volcano Alert Level (VAL) to Advisory. Retrospective analysis of satellite data acquired on 10 September revealed small ash deposits on the N flank of Mount Cerberus, possibly associated with two bursts of tremor recorded on 8 September (figure 5). This new information, coupled with intensifying seismicity and a strong tremor signal recorded at 1249 on 17 September, resulted in AVO raising the ACC to Orange and the VAL to Watch. Seismicity remained elevated on 18 September with nearly constant tremor recorded by local sensors. At the same time, no ash emissions were observed in cloudy satellite images and no eruptive activity was recorded on regional pressure sensors at Adak.

Figure 1. Minor ash deposits can be seen on the south and west flanks of the N cone of Mount Cerberus, Semisopochnoi Island, in this ESA Sentinel-2 image from 1200 on 10 September 2018. Also note probable minor steam emissions obscuring the crater of the N cone. Image courtesy of AVO.

During 19-25 September 2018 seismicity remained elevated, alternating between periods of continuous and intermittent bursts of tremor. Tremor bursts at 1319 on 21 September and at 1034 on 22 September produced airwaves detected on a regional infrasound array on Adak Island; no ash emissions were identified above the low cloud deck in satellite data, and the infrasound detections likely reflected an atmospheric change instead of volcanic activity.

Seismicity remained elevated during 3-9 October 2018, with intermittent bursts of tremor. No volcanic activity was detected in infrasound or satellite data. On 11 October satellite data indicated partial erosion of a tephra cone in the crater of Cerberus's N cone. A crater lake about 90 m in diameter filled the vent. The data also suggested that the vent had not erupted since 1 October. Seismicity remained elevated and above background levels. The next day AVO lowered the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory, noting the recent satellite data results and lack of tremor recorded during the previous week. AVO reported that unrest continued during 11-24 October.

An eruptive event began at 2047 on 25 October 2018, identified based on seismic data; strong volcanic tremor lasted about 20 minutes and was followed by 40 minutes of weak tremor pulses. A weak infrasound signal was detected by instruments on Adak Island. The Aviation Color Code was raised to Orange (the second highest level on a four-color scale) and Volcano Alert Level was raised to Watch (the second highest level on a four-level scale). A dense meteorological cloud deck prevented observations below 3 km, but a diffuse cloud was observed in satellite data rising briefly above the cloud deck, though it was unclear if it was related to eruptive activity. Tremor ended after the event, and seismicity returned to low levels.

Small explosions were detected by the seismic network at 2110 and 2246 on 26 October 2018, and 0057 and 0603 on 27 October. No ash clouds were identified in satellite data, but the volcano was obscured by high meteorological clouds. Additional small explosions were detected in seismic and infrasound data during 28-29 October; no ash clouds were observed in partly-cloudy-to-cloudy satellite images.

AVO reported on 31 October 2018 that unrest continued. Two small explosions were detected, one just before 0400 and the other around 1000. Satellite views were obscured by clouds at the time, and no ash clouds were observed. Unrest continued through 1 November, at which time the satellite link and the seismic line failed. On 21 November the ACC was lowered to Yellow and the VAL was lowered to Advisory.

Geologic Background. Semisopochnoi, the largest subaerial volcano of the western Aleutians, is 20 km wide at sea level and contains an 8-km-wide caldera. It formed as a result of collapse of a low-angle, dominantly basaltic volcano following the eruption of a large volume of dacitic pumice. The high point of the island is 1221-m-high Anvil Peak, a double-peaked late-Pleistocene cone that forms much of the island's northern part. The three-peaked 774-m-high Mount Cerberus volcano was constructed during the Holocene within the caldera. Each of the peaks contains a summit crater; lava flows on the northern flank of Cerberus appear younger than those on the southern side. Other post-caldera volcanoes include the symmetrical 855-m-high Sugarloaf Peak SSE of the caldera and Lakeshore Cone, a small cinder cone at the edge of Fenner Lake in the NE part of the caldera. Most documented historical eruptions have originated from Cerberus, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone within the caldera could have been active during historical time.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://dggs.alaska.gov/).

Japan's 24-km-wide Asosan caldera on the island of Kyushu has been active throughout the Holocene. Nakadake has been the most active of 17 central cones within the caldera for 2,000 years. Historical eruptions have been primarily basaltic to basaltic-andesitic ash eruptions, with periodic Strombolian activity, all from Nakadake Crater 1. The most recent major eruptive episode began in late November 2014 and continued through 1 May 2016. Another eruption, with the largest ash plume in 20 years, occurred on 8 October 2016. Asosan remained quiet until renewed activity from Crater 1 began in mid-April 2019; it is covered in this report, through the end of June 2019. The Japan Meteorological Agency (JMA) provides monthly reports of activity; the Tokyo Volcanic Ash Advisory Center (VAAC) issues aviation alerts reporting on possible ash plumes.

Asosan remained quiet during 2017 and 2018 with steam plumes rising a few hundred meters from Crater 1 and low levels of SO₂ emissions; a warm acidic lake was present within the crater. Fumarolic activity from two areas on the S and SW wall of the crater rim generated occasional thermal anomalies in satellite data and incandescence at night. A brief period of increased seismicity was reported in mid-March 2019. An increase in seismic amplitude on 14 April 2019 preceded a small explosion on 16 April; it produced an ash plume which rose 200 m above the crater rim and drifted NW. It was followed by additional small explosions on 19 April. A new explosion on 3 May produced minor ashfall in adjacent communities; ash emissions were reported multiple times during May with plumes reaching 1,400 m above the crater rim. No additional ash emissions were reported in June.

Activity during 2017 and 2018. JMA reported that no eruptions occurred during 2017. Amplitudes of volcanic tremor increased somewhat during March but were generally low for the rest of the year. The earthquake hypocenters were mostly located near the active crater at around sea level. SO2 emissions were slightly less than 1,000 tons per day (t/d) from January through April; for the rest of the year they ranged from 600 to 2,500 t/d. The Alert Level had been lowered from 2 to 1 on 7 February 2017 where it remained throughout the year. Steam plumes generally rose no more than 600 m above the active crater rim (figure 42). JMA noted that from January to June they often observed crater incandescence at night with a high-sensitivity surveillance camera; Sentinel-2 satellite images also captured thermal anomalies a few times (figure 43). The green lake inside the crater persisted throughout the year with water temperatures of 50-60°C. Two fumaroles were present with high-temperature gas emissions on the SW and S crater walls. Temperatures at the S crater wall were over 600°C from February to May; they decreased to 320-560°C during the rest of the year (figure 44). Sulfur deposits were visible around the SW crater wall fumarole during July.

Figure 42. Steam plumes that rose around 600 m above Nakadake Crater 1 at Asosan were typical activity throughout 2017. Images taken with JMA webcam on 9 June (top left), 22 August (top right), 12 November (bottom left), and 20 December (bottom right) 2017. Courtesy of JMA (Aso volcano monthly activity reports, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 43. Sentinel-2 images captured thermal anomalies at the S rim of the green lake at Asosan's Nakadake Crater 1 on 16 February (left) and 27 May 2017 (right). JMA reported that incandescence was occasionally visible during the night from January-June from the same area. Courtesy of Sentinel Hub Playground.

Figure 44. High-temperature gas and steam from fumaroles on the S wall of the Nakadake Crater 1 at Asosan on 24 August (top) and 17 November 2017 (bottom) were persistent all year, with temperatures ranging from 300 to over 600°C. The green lake inside the crater persisted throughout the year as well with water temperatures of 50-60°C. Courtesy of JMA (Aso volcano monthly activity reports, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

The Alert Level did not change at Asosan during 2018, and no eruptions were reported. Sulfur dioxide emissions fluctuated between 400 and 1,800 t/d throughout the year. Steam plumes generally rose less than 500 m above the active crater (figure 45); incandescence was observed at night during May-October and sometimes observed in satellite imagery as thermal anomalies (figure 46). The temperature of the green lake inside the crater ranged from 58 to 75°C throughout the year. The thermal anomaly on the S wall of the crater was consistently in the 300-500°C range, and had a high temperature in April of 580°C; in December the high temperature had risen to 738°C (figure 47). A brief increase in the number of isolated tremors occurred during March, with 1,044 reported on 4 March, exceeding the previous maximum of 1,000 on 27 October 2014. Seismicity also increased briefly during June, with more than 400 events reported each day on 8, 18, and 20 June. The Minami Aso village Yoshioka fumarole zone, located about 5 km W of Nakadake Crater 1, continued to produce modest steam plumes throughout 2017 and 2018 (figure 48).

Figure 45. Typical steam plumes at Asosan during 2018 rose around 500 m above the Nakadake Crater 1. Images are from 4 March (top left), 22 July (top right), 17 August (lower left), and 13 September 2018 (lower right). Courtesy of JMA (Aso volcano monthly activity reports, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 46. Nighttime incandescence was reported by JMA during May-October 2018 from the S rim of Nakadake Crater 1 at Asosan; Sentinel-2 satellite images (bands 12, 4, 2) captured thermal anomalies from the same area numerous times during 2018 including on 16 June (top left), 26 July and 19 September (middle row), and 18 and 23 November (bottom row). JMA photographed incandescence at night on 17 July 2018 at the S fumarole area (top right). Courtesy of Sentinel Hub Playground and JMA (Aso volcano Monthly Report for July 2018).

Figure 47. The "Green Tea Pond" inside Nakadake Crater 1 at Asosan had temperatures that ranged from 58 to 75°C during 2018 (top row, 26 March 2018); the thermal anomaly on the S wall of the crater consistently had temperatures measured in the 300-500°C range and the SW fumarole area had somewhat lower temperatures (bottom row, 22 June 2018). Courtesy of JMA (monthly Asosan reports for March, May, and June 2018).

Figure 48. The Minami Aso village Yoshioka fumarole zone, located about 5 km W of Nakadake Crater 1 at Asosan, continued to produce modest steam plumes throughout 2017 and 2018. It is shown here on 20 December 2017 (top) and 12 March 2018 (bottom). Courtesy of JMA (December 2017 and March 2018 monthly volcano reports).

Activity during 2019. Steam plumes rose to 800 m above the crater rim during January 2019. Overall activity increased slightly during February; SO₂ emissions peaked at 2,200 t/d early in the month; they ranged from 800 to 1,800 t/d for most of the month. The amplitude of volcanic tremor also increased slightly during February. A further increase in tremor amplitude on 11 March 2019 prompted JMA to raise the Alert Level from 1 to 2 the following morning. Volcanic tremor amplitude decreased on 15 March; JMA determined that activity had decreased, and the Alert Level was lowered back to 1 on 29 March 2019. The amount of water in the crater decreased significantly between 27 February and 20 March, exposing part of the crater floor.

The surface temperature of the lake rose during the first part of 2019; it was 78°C in February and 84°C in March. Steam plumes rose to 1,200 m above the crater rim during March and April. SO₂ emissions rose to 4,500 t/d on 12 March but dropped to a lower range of 1,300-2,400 for the rest of the month. Another surge in SO₂ emissions on 12 April 2019 to 3,600 t/d prompted a special report from JMA the following day. SO₂ emissions varied from about 1,700 to 4,100 t/d during the month; values remained high during the second half of the month. JMA noted that the color of the water in the lake inside Nakadake Crater 1 changed from green to gray after 4 April. Fountains of muddy water were periodically observed; they reached 15 m high on 9 April. The temperatures of both the lake (82°C) and around the two fumarole areas (S area about 530°C, SW area about 310°C) remained constant during April and similar to March.

A large increase in the amplitude of volcanic tremor early on 14 April 2019 prompted JMA to raise the Alert Level from 1 to 2 later in the day. The epicenters of the earthquakes were very shallow, located within 1 km beneath the crater. A small eruption occurred at 1828 on 16 April at Nakadake Crater 1; it produced a gray and white plume that rose 200 m above the crater rim and was the first eruption since 8 October 2016 (figure 49). Incandescence was observed inside the crater on 3 and 17 April. The amplitude of seismic tremors decreased on 18 April. Three very small eruptions on 19 April produced ash and steam plumes that rose 500 m above the crater rim. During a site visit that day JMA measured a high-temperature area that produced incandescence from the bottom of the crater at night (figure 50).

Figure 49. The first eruption since October 2016 at Nakadake Crater 1 at Asosan on 16 April 2019 sent an ash plume 200 m above the crater rim (top). Incandescent gas appeared on the crater floor the next day (bottom). Courtesy of JMA (Aso volcano monthly activity reports, April 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 50. Three small explosions on 19 April 2019 at Asosan's Nakadake Crater 1 produced small ash emissions that rose 500 m above the crater rim (top). A strong thermal signal also appeared from the bottom of the crater. Courtesy of JMA (Aso volcano monthly activity reports, April 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

A new eruption began at 1540 on 3 May that lasted until 0620 on 5 May (figure 51). Initially the ash plume rose 600 m above the crater rim, but a few hours later the volume of ash increased, and the plume reached 2 km above the crater rim for a brief period. Incandescence was visible from the webcam. The Tokyo VAAC reported the ash plume at 3 km altitude drifting SE on 3 May. Later in the day it rose to 3.7 km altitude and drifted SW. During a field survey the following day (4 May) JMA reported a steam and ash plume rising from the center of the active crater. The infrared thermal imaging camera recorded the temperature of the plume at about 500°C (figure 52).

Figure 51. An explosion at Asosan's Nakadake Crater 1 on 3 May 2019 produced an ash plume that reached 2 km above the crater rim (top) and incandescence visible from the webcam (bottom). Courtesy of JMA (Aso volcano monthly activity reports, April 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 52. During a site visit on 4 May 2019, staff from JMA witnessed an ash and steam plume rising from the bottom of Nakadake Crater 1 at Asosan (top). The infrared thermal imaging camera recorded the temperature of the plume at about 500°C (bottom). Courtesy of JMA (Aso volcano monthly activity reports, May 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Ash fell on the S flank, and a small amount of ashfall on 4 May was confirmed by evidence on a car windshield in Takamori Town (6 km S), Kumamoto Prefecture (figure 53). Ashfall was also reported in Takamori-machi, Minami Aso village (9 km SW), and part of Yamato-cho (25 km SW), also in the Kumamoto Prefecture. SO₂ emissions were measured as high as 4,000 t/d on 4 May. Additional explosions with ash plumes were reported from Asosan on 9, 12-16, 29, and 31 May; the plumes rose from 200 to 1,400 m above the crater rim but were not visible in satellite imagery. The TROPOMI instrument on the Sentinel-5 satellite captured SO₂ plumes on 3 and 26 May 2019 (figure 54).

Figure 53. Ashfall was reported on 4 May 2019 in Takamori Town, Kumamoto Prefecture, from the eruption at Asosan's Nakadake Crater 1 on 3 May 2019. Courtesy of JMA (Aso volcano monthly activity reports, May 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 54. Plumes of SO2 from Asosan were recorded by the TROPOMI instrument on the Sentinel-5P satellite on 3 (left) and 26 (right) May 2019. Courtesy of NASA Goddard Space Flight Center.

Steam plumes rose to 1,700 m above the crater rim during June 2019 (figure 55). During field visits on 6 and 25 June diffuse ash emissions were observed rising from the center of the active crater, but they did not extend significantly above the crater rim (figure 56). The maximum temperature of the plume was measured at about 340°C with a thermal imaging camera. Almost all of the water in the crater bottom had evaporated since early May; incandescence continued to be observed within the crater at night with the high-resolution webcam (figure 57).

Figure 55. Steam plumes rose to 1,700 m above the crater rim at Asosan's Nakadake Crater 1 on 10 June 2019. Courtesy of JMA (Aso volcano monthly activity reports, June 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 56. Plumes of gas and minor ash were visible at Asosan's Nakadake Crater 1 during site visits by JMA on 6 (left) and 25 (right) June 2019. Courtesy of JMA (Aso volcano monthly activity reports, June 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 57. Incandescent gas was visible from the vent at Asosan's Nakadake Crater 1 on 18 (left) and 25 (right) June 2019. Courtesy of JMA (Aso volcano monthly activity reports, June 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Geologic Background. The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

The Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo is part of the western branch of the East African Rift System. Nyamuragira (or Nyamulagira), a high-potassium basaltic shield volcano on the W edge of VVP, includes a lava field that covers over 1,100 km² and contains more than 100 flank cones in addition to a large central crater (see figure 63, BGVN 42:06). A lava lake that had been active for many years emptied from the central crater in 1938. Numerous flank eruptions were observed after that time, the most recent during November 2011-March 2012 on the NE flank. This was followed by a period of degassing with unusually SO₂-rich plumes from April 2012 through April 2014 (BGVN 42:06). The lava lake reappeared during July 2014-April 2016 and November 2016-May 2017, producing a strong thermal signature. After a year of quiet, a new lava lake appeared in April 2018, reported below (through May 2019) with information provided by the Observatoire Volcanologique de Goma (OVG), MONUSCO (the United Nations Organization working in the area), and satellite data and imagery from multiple sources.

Fresh lava reappeared inside the summit crater in mid-April 2018 from a lava lake and adjacent spatter cone. Satellite imagery and very limited ground-based observations suggested that intermittent pulses of activity from both sources produced significant lava flows within the summit crater through April 2019 when the strength of the thermal signal declined significantly. Images from May 2019 showed a smaller but persistent thermal anomaly within the crater.

Activity from October 2017-May 2019. Indications of thermal activity tapered off in May 2017 (BGVN 42:11). On 20 October 2017 OVG released a communication stating that a brief episode of unspecified activity occurred on 17 and 18 October, but the volcano returned to lower activity levels on 20 October. There was no evidence of thermal activity during the month. The volcano remained quiet with no reports of thermal activity until April 2018 (figure 73).

Figure 73. Sentinel-2 satellite images (bands 12, 4, 2) indicated no thermal activity at Nyamuragira on 19 November (top left), 14 December 2017 (top right) and 18 January 2018 (bottom). However, Nyiragongo (about 13 km SE) had an active lava lake with a gas plume drifting SW on 18 January 2018 (bottom right). Courtesy of Sentinel Hub Playground.

OVG reported the new lava emissions beginning on 14 April 2018 as appearing from both the lava lake and a small adjacent spatter cone (figure 74). The first satellite image showing thermal activity at the summit appeared on 18 April 2018 (figure 75) and coincided with the abrupt beginning of strong MIROVA thermal signals (figure 76). MODVOLC thermal alerts also first appeared on 18 April 2018. An image of the active crater taken on 9 May 2018 showed the lake filled with fresh lava and two adjacent incandescent spatter cones (figure 77).

Figure 74. Fresh lava reappeared at Nyamuragira's crater during April 2018 from the lava lake (left) and the adjacent small spatter cone (right). Courtesy of OVG (Republique Democratique du Congo, Ministere de la Recherche Scientifique, Observatoire Volcanologique de Goma, Direction Generale Goma, Rapport Avril 2018).

Figure 75. The first satellite image (bands 12, 4, 2) indicating renewed thermal activity at the Nyamuragira crater appeared on 18 April 2018; the signal remained strong a few weeks later on 3 May 2018. Courtesy of Sentinel Hub Playground.

Figure 76. A strong thermal signal appeared in the MIROVA graph of Log Radiative Power on 18 April 2018 for Nyamuragira, indicating a return of the lava lake at the summit crater. Courtesy of MIROVA.

Figure 77. Fresh lava filled the lake inside the crater at Nyamuragira on 9 May 2018. Two spatter cones were incandescent with gas emissions. Courtesy of OVG (Republique Democratique du Congo, Ministere de la Recherche Scientifique, Observatoire Volcanologique de Goma, Direction Generale Goma, Rapport Mai 2018).

Satellite images confirmed that ongoing activity from the lava lake remained strong during June -September 2018 (figure 78). A mission to Nyamuragira was carried out by helicopter provided by MONUSCO on 20 July 2018; lava lake activity was observed along with gas emissions from the small spatter cone (figure 79). OVG reported increased volcanic seismicity during 1-3 and 10-17 September 2018, and also during October, located in the crater area, mostly at depths of 0-5 km.

Figure 78. Sentinel-2 satellite images (bands 12, 4, 2) confirmed that ongoing activity from the lava lake at Nyamuragira remained strong during June-September 2018, likely covering the crater floor with a significant amount of fresh lava. Image are from 12 June (top left), 7 July (top right), 17 July (middle left), 22 July (middle right), 11 August (bottom left), and 20 September (bottom right). Courtesy of Sentinel Hub Playground.

Figure 79. The crater at Nyamuragira on 20 July 2018 had an active lava lake and adjacent incandescent spatter cone with gas emissions. Courtesy of OVG (Republique Democratique du Congo, Ministere de la Recherche Scientifique, Observatoire Volcanologique de Goma, Direction Generale Goma, Rapport Juillet 2018).

Personnel from OVG and MONUSCO (United Nations Organization Stabilization Mission in DR Congo) made site visits on 11 October and 2 November 2018 and concluded that the level of the active lava lake had increased during that time (figure 80). On 2 November OVG measured the height from the base of the active cone to the W rim of the crater as 58 m (figure 81).

Figure 80. OVG scientists reported a rise in the lake level between site visits to the Nyamuragira crater on 11 October (top) and 2 November 2018 (bottom). Top image courtesy of MONUSCO and Culture Vulcan, bottom image courtesy of OVG (Republique Democratique du Congo, Ministere de la Recherche Scientifique, Observatoire Volcanologique de Goma, Direction Generale Goma, Rapport Octobre 2018).

Figure 81. On 2 November 2018 scientists from OVG measured the height from the base of the active cone to the W rim of the crater as 58 m. Courtesy of OVG (Republique Democratique du Congo, Ministere de la Recherche Scientifique, Observatoire Volcanologique de Goma, Direction Generale Goma, Rapport Octobre 2018).

Seismicity remained high during November 2018 but decreased significantly during December. Instrument and access issues in January 2019 prevented accurate assessment of seismicity for the month. The lava lake remained active with periodic surges of thermal activity during November 2018-March 2019 (figure 82). Multiple images show incandescence in multiple places within the crater, suggesting significant fresh overflowing lava.

Figure 82. The active lava lake at Nyamuragira produced strong thermal signals from November 2018 through March 2019 that were recorded in Sentinel-2 satellite images (bands 12, 4, 2). Several images suggest fresh lava cooling around the rim of the crater in addition to the active lake. A relatively cloud-free day on 19 November 2018 (top left) revealed no clear thermal signal, but a strong signal was recorded on 29 November (top right) despite significant cloud cover. Images from 13 and 28 January 2019 (second row) both showed evidence of incandescent lava in multiple places within the crater. The thermal signal was smaller and focused on the center of the crater on 12 and 27 February 2019 (third row). Images taken on 9 and 19 March 2019 clearly showed incandescent material at the center of the crater and around the rim (bottom row). Courtesy of Sentinel Hub Playground.

On 12 April 2019 a Ukrainian Aviation Unit supported by MONUSCO provided support for scientists visiting the crater for observations and seismic analysis. Satellite data confirmed ongoing thermal activity into May, although the strength of the signal appeared to decrease (figure 83). MODVOLC thermal alerts ceased after 8 April, and the MIROVA thermal data also confirmed a decrease in the strength of the thermal signal during April 2019 (figure 84).

Figure 83. Sentinel-2 satellite data (bands 12, 4, 2) confirmed ongoing thermal activity at Nyamuragira into May 2019. The thermal anomalies on 18 April (left) and 3 May (right) 2019 were smaller than those recorded during previous months. Courtesy of Sentinel Hub Playground.

Figure 84. The MIROVA graph of thermal activity (log radiative power) at Nyamuragira from 16 July 2018 through April 2019 showed near-constant levels of high activity through April 2019 when it declined. This corresponded well with satellite and ground-based observations. Courtesy of MIROVA.

Geologic Background. Africa's most active volcano, Nyamuragira, is a massive high-potassium basaltic shield about 25 km N of Lake Kivu. Also known as Nyamulagira, it has generated extensive lava flows that cover 1500 km2 of the western branch of the East African Rift. The broad low-angle shield volcano contrasts dramatically with the adjacent steep-sided Nyiragongo to the SW. The summit is truncated by a small 2 x 2.3 km caldera that has walls up to about 100 m high. Historical eruptions have occurred within the summit caldera, as well as from the numerous fissures and cinder cones on the flanks. A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption. Historical lava flows extend down the flanks more than 30 km from the summit, reaching as far as Lake Kivu.

Information Contacts: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; Katcho Karume, Director; Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MONUSCO, United Nations Organization Stabilization Mission in the DR Congo (URL: https://monusco.unmissions.org/en/, Twitter: @MONUSCO); Cultur Volcan, Journal d'un volcanophile (URL: https://laculturevolcan.blogspot.com), Twitter: @CultureVolcan).

The 16-km-wide Tengger Caldera in East Java, Indonesia is a massive volcanic complex with numerous overlapping stratovolcanos (figure 11). Mount Bromo is a pyroclastic cone that lies within the large Sandsea Caldera at the northern end of the complex (figure 12) and has erupted more than 20 times during each of the last two centuries. It is part of the Bromo Tengger Semeru National Park (also a UNESCO Biosphere Reserve) and is frequently visited by tourists. The last eruption from November 2015 to November 2016 produced hundreds of ash plumes that rose as high as 4 km altitude; some of them drifted for hundreds of kilometers before dissipating and briefly disrupted air traffic. Only steam and gas plumes were observed at Mount Bromo from December 2016 to February 2018 when a new series of explosions with ash plumes began; they are covered in this report with information provided by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM) and the Darwin Volcanic Ash Advisory Centre (VAAC). Copyrighted ground and drone-based images from Øystein Lund Andersen have been used with permission of the photographer.

Figure 11. The Tengger Caldera viewed from the north Mount Bromo issuing steam in the foreground and Semeru volcano in the background on 30 September 2018. Courtesy of Øystein Lund Andersen, used with permission.

Figure 12. Aerial view of the Bromo Cone in Tengger Caldera seen from the west on 30 September 2018. Courtesy of Øystein Lund Andersen, used with permission.

PVMBG lowered the Alert Level at Bromo on 21 October 2016 from III to II near the end of an eruptive episode lasting nearly a year. The last VAAC report was issued on 12 November 2016 (BGVN 41:12) noting that the last ash emission had been observed the previous day drifting NW at 3 km altitude. Throughout 2017 and 2018 Bromo remained at Alert Level II, with no unusual activity described by PVMBG. During 1-2 September 2018, a wildfire in the Bromo Tengger Semeru National Park burned 65 hectares of savannah (figure 13); the fire produced 12 MODVOLC thermal alerts around the Tengger Caldera rim. No reports of increased volcanic activity were issued by PVMBG during the period.

Figure 13. A wall of fire in the Bromo Tengger Semeru National Park savanna during 1-2 September 2018 produced thermal alerts that were not related to volcanic activity at the Bromo Cone in Tengger Caldera. Image courtesy of the park authority, reported by Mongabay. MODVOLC thermal alerts courtesy of Hawai'i Institute of Geophysics and Planetology (HIGP).

After slightly more than two years of little activity other than gas and steam plumes, ash emissions resumed from the Bromo Cone on 18 February 2019. After a brief pause, a new explosion on 10 March marked the beginning of a series of near-daily ash emissions that lasted for the rest of March, producing ash plumes that rose to altitudes ranging from 3.0 to 5.2 km and drifted in many different directions. A new series of ash emissions began on 6 April, rising to 3 km and also drifting in multiple directions. Ash emission density decreased during the month; plumes were only rising a few hundred meters above the summit by the end of April and consisted of mostly steam and moderate amounts of ash.

Activity during February-April 2019. PVMBG reported that at 0600 on 18 February 2019 an eruption at Tengger Caldera's Bromo Cone generated a dense white-and-brown ash plume that rose 600 m and drifted WSW. The plume was not visible in satellite imagery, according to the Darwin VAAC. The Alert Level remained at 2 (on a scale of 1-4). After a few weeks of quiet a new explosion on 10 March (local time) produced a white, brown, and gray ash plume that rose 600 m above the summit; the plume was visible in satellite imagery extending SW. Increased tremor amplitude was also reported on 10 March. A new emission the next morning produced similar ash plumes that drifted S, SW, and W at 3 km altitude. On the morning of 12 March (local time) a continuous ash plume was observed in satellite imagery at 3.4 km altitude drifting SW. The plume drifted counterclockwise towards the S, E, and NE throughout the day and continued to drift NE and SE on 13 March. The altitude of the plume was reported at 4.3 km later that day based on a pilot report.

Continuous brown, gray, and black ash emissions were reported by PVMBG during 14-19 March at altitudes ranging from 3 to 3.9 km; they drifted generally NE to NW. Ashfall was noted around the crater and downwind a short distance. The Darwin VAAC reported continuous ash emissions to 5.2 km altitude drifting SE on 20 March. It was initially reported by a pilot and partially discernable in satellite imagery before dissipating. Ongoing ash emissions of variable densities and colors ranging from white to black were intermittently visible in satellite imagery and confirmed in webcam and ground reports at around 3.0 km altitude during 21-25 March (figures 14-17). Ashfall impacted the closest villages to Bromo, including Cemara Lawang (30 km NW), which was covered by a thin layer of ash. A few trees in the area were toppled over by the weight of the ash. The plume altitude increased slightly on 26 March to 3.7-3.9 km, drifting N and NE. The higher altitude plume dissipated early on 28 March, but ash emissions continued at 3.0 km for the rest of the day.

Figure 14. Ash drifted NNE from the Bromo Cone in Tengger Caldera on 23 March 2019. Courtesy of Øystein Lund Andersen (drone image), used with permission.

Figure 15. Ash drifted N from the Bromo Cone in Tengger Caldera on 23 March 2019. The Batok Cone is on the right, Segera Wedi is behind Bromo, and Semeru is in the far background. Courtesy of Øystein Lund Andersen, used with permission.

Figure 16. A few trees toppled from ashfall in the vicinity of the Bromo Cone in Tengger Caldera on 24 March 2019. Courtesy of Øystein Lund Andersen, used with permission.

Figure 17. Ash plumes from the Bromo Cone in Tengger Caldera on 24 March 2019 caused ashfall in communities as far as 30 km away. View is from the floor of the Sandsea Caldera. Courtesy of Øystein Lund Andersen, used with permission.

After just a few days of quiet, new ash emissions rising to 3.0 km altitude and drifting SE were reported by both PVMBG (from the webcam) and the Darwin VAAC on 6 April 2019. By the next day the continuous ash emissions were drifting N, then E during 8-10 April, and S during 11 and 12 April. A new emission seen in the webcam was reported by the Darwin VAAC on 15 April (UTC) that rose to 3.0 km and drifted W. Ash plumes were intermittently visible in either webcam or satellite imagery until 17 April rising 500-1,000 m above the crater; from 19-25 April only steam plumes were reported rising 300-500 m above the summit. A minor ash emission was reported from the webcam on 26 April that rose to 3.0 km altitude and drifted NE for a few hours before dissipating. PVMBG reported medium density white to gray ash plumes that rose 400-600 m above the crater for the remainder of the month.

Geologic Background. The 16-km-wide Tengger caldera is located at the northern end of a volcanic massif extending from Semeru volcano. The massive volcanic complex dates back to about 820,000 years ago and consists of five overlapping stratovolcanoes, each truncated by a caldera. Lava domes, pyroclastic cones, and a maar occupy the flanks of the massif. The Ngadisari caldera at the NE end of the complex formed about 150,000 years ago and is now drained through the Sapikerep valley. The most recent of the calderas is the 9 x 10 km wide Sandsea caldera at the SW end of the complex, which formed incrementally during the late Pleistocene and early Holocene. An overlapping cluster of post-caldera cones was constructed on the floor of the Sandsea caldera within the past several thousand years. The youngest of these is Bromo, one of Java's most active and most frequently visited volcanoes.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Øystein Lund Andersen (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: http://www.oysteinlundandersen.com); Mongabay, URL: https://news.mongabay.com/2018/09/fires-tear-through-east-java-park-threatening-leopard-habitat/.

Eruptive activity has been ongoing at Bagana since February 2000, and frequently active for over 150 years. Due to the remote location of this volcano, the most reliable observations of activity come from the identification of ash plumes in satellite imagery by the Darwin Volcanic Ash Advisory Centre (VAAC) and thermal anomalies from satellite infrared sensors.

Since July 2016 (BGVN 41:07), the Darwin VAAC issued aviation warnings of ash plumes almost every week through mid-June 2017. The plumes typically rose to between 1.8 and 3.4 km; the most commonly reported altitude of the plume was about 2.1 km. The plumes drifted in multiple directions depending on the local wind patterns. Drift directions were not always reported, but a few reached 110-120 km, and one was observed as far as 160 km away on 7 September 2016.

MODIS data processed by the MIROVA algorithm (figure 28) reinforce the Darwin VAAC reports of a nearly continuous eruption since July 2016 through mid-June 2017. Frequent MODVOLC thermal alerts, also based on MODIS satellite-based data, corroborate the MIROVA analysis.

Figure 28. Thermal anomalies at Bagana shown on a MIROVA plot (Log Radiative Power) for the year ending 12 June 2017. Courtesy of MIROVA.

Geologic Background. Bagana volcano, occupying a remote portion of central Bougainville Island, is one of Melanesia's youngest and most active volcanoes. This massive symmetrical cone was largely constructed by an accumulation of viscous andesitic lava flows. The entire edifice could have been constructed in about 300 years at its present rate of lava production. Eruptive activity is frequent and characterized by non-explosive effusion of viscous lava that maintains a small lava dome in the summit crater, although explosive activity occasionally producing pyroclastic flows also occurs. Lava flows form dramatic, freshly preserved tongue-shaped lobes up to 50 m thick with prominent levees that descend the flanks on all sides.

Information Contacts: Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

Activity at Bulusan typically has included phreatic explosions from the summit crater and flank vents, ash-and-steam plumes, and minor ashfall in nearby villages (BGVN 41:03, 42:02). The danger zone was expanded in October 2016 when a fissure extended 2 km down the upper S flank that was the source of multiple phreatic explosions (figure 10, and see BGVN 42:02). During the first eight months of 2017, eruptive activity included similar episodes on 2 March and 5 June. Information was provided by the Philippine Institute of Volcanology and Seismology (PHIVOLCS). Throughout the reporting period of 1 January-8 September 2017 the Alert Level remained at 1, indicating a low level of volcanic unrest and a 4-km-radius Permanent Danger Zone (PDZ).

Figure 10. A phreatic ash explosion from the SE vent at Bulusan on 17 October 2016 lasted 24 minutes. White steam plumes can be seen rising from other vents. Photo by Drew Zuñiga and provided by 2D Albay, as published in The Philippine Star (18 October 2016).

According to PHIVOLCS, a weak phreatic eruption occurred at 1357 on 2 March 2017. The event was recorded by the seismic network as an explosion-type earthquake followed by short-duration tremor that lasted approximately 26 minutes. Visual observations were obscured by weather clouds, although a small steam plume rising from the SE vent was recorded by a webcam.

On 5 June 2017 another weak phreatic eruption was recorded at 1029 by the seismic network for 12 minutes. The eruption again could not be visually observed due to dense weather clouds covering the summit. Minor ashfall, a sulfuric odor, and a rumbling sound were reported in the barangays (neighborhoods) of Monbon and Cogon, while sulfuric odor was noted in the barangay of Bolos. These three neighborhoods are within the municipality of Irosin, about 8 km SSW of the volcano.

According to a news account (Manila Bulletin), precise leveling data obtained during 29 January to 3 February 2017 indicated deflationary changes since October 2016. PHIVOLCS reported that precise leveling data obtained during 14-23 June 2017 indicated inflation since February 2017. According to PHIVOLCS, continuous GPS measurements have indicated an inflationary trend since July 2016.

Sulfur dioxide emissions on 31 July and 20 August, reported by PHIVOLCS, averaged 82 tonnes/day, which according to a news account (Manila Bulletin) was the same as measured on 29 April 2017. The seismic monitoring network recorded three volcanic earthquakes on 7-8 September. Weak steam plumes from the active vents rose to 50 meters and drifted SW.

Geologic Background. Luzon's southernmost volcano, Bulusan, was constructed along the rim of the 11-km-diameter dacitic-to-rhyolitic Irosin caldera, which was formed about 36,000 years ago. It lies at the SE end of the Bicol volcanic arc occupying the peninsula of the same name that forms the elongated SE tip of Luzon. A broad, flat moat is located below the topographically prominent SW rim of Irosin caldera; the NE rim is buried by the andesitic complex. Bulusan is flanked by several other large intracaldera lava domes and cones, including the prominent Mount Jormajan lava dome on the SW flank and Sharp Peak to the NE. The summit is unvegetated and contains a 300-m-wide, 50-m-deep crater. Three small craters are located on the SE flank. Many moderate explosive eruptions have been recorded since the mid-19th century.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), Department of Science and Technology, University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/); Manila Bulletin (URL: http://mb.com.ph/); Philippine Star (URL: http://www.philstar.com/).

Frequent historical eruptions at México's Volcán de Colima (Volcán Fuego) date back to the 16th century and include vulcanian and phreatic explosions, lava flows, large debris avalanches, and pyroclastic flows. The latest eruptive episode began in January 2013. Extensive activity in 2015 included near-constant ash plumes with extensive ashfall, lava flows, and pyroclastic flows (BGVN 41:01). The eruption continued throughout 2016 until the last ash-bearing explosion was reported on 7 March 2017. This report covers the activity through June 2017. Most of the information for this report was gathered from the Unidad Estatal de Protección Civil de Colima (UEPCC), the Centro Universitario de Estudios e Investigaciones de Vulcanologia, Universidad de Colima (CUEIV-UdC), and the Washington Volcanic Ash Advisory Center (VAAC).

Colima was very active from January through April 2016 with hundreds of ash emissions, and a slow-growing lava dome that was first observed on 19 February. Activity decreased during May-September, although multiple explosions with ash plumes still took place most weeks during the period. On 30 September, the lava dome overflowed the crater rim, and sent a slow-moving lava flow and incandescent material down the SW flank. The lava flow continued to grow, reaching over 2 km in length by the end of October. A second lava flow appeared in mid-November, and advanced 1.7 km by early December. Strong ash-bearing explosions during December 2016-January 2017 sent plumes to heights of 4-6 km above the crater. Activity decreased during the second half of February; the last ash-bearing explosion was reported on 7 March 2017. Decreasing seismicity and minor landslides were reported through June 2017 with no further eruptive activity.

Incandescent activity during explosions in January 2016 sent glowing blocks down the flanks of Colima along with spectacular lightning in the ash plumes (figure 116). Ash emissions continued at Colima at a very high rate of multiple daily events, similar to December 2015 (figure 117). The Washington VAAC issued multiple advisories nearly every day during the month with information based on satellite imagery, wind data, webcam images, and notices from the México City Meteorological Watch Office (MWO). The ash plumes rose to altitudes of 4.3-6.7 km and most commonly drifted N or E. They generally drifted a few tens of kilometers before dissipating, but a few were still visible as far as 200 km from the summit.

Figure 116. Eruption of ash plume and incandescent material at Colima on 3 January 2016. Courtesy of Volcano Discovery.

Figure 117. Ash eruption at Colima on 10 January 2016. Image from the Webcams de México Colima webcam located at the Laguna de Carrizalillos in Comala, about 25 km SW of the summit.

Multiple daily ash advisories from the Washington VAAC continued during 1-9 February. They resumed on 14 February, and were intermittent for the rest of the month with similar altitudes and drift directions as those observed during January, but at a slightly lower frequency, decreasing towards the end of the month. On 19 February, CUEIV-UdC researcher Nick Varley observed a lava dome emerging from the floor of the crater (figure 118) during a helicopter overflight. It was estimated to be 25-30 m in diameter and 10 m high inside the almost 300-m-diameter, 50-m-deep summit crater. By 29 February, the dome had increased in size (figure 119), and fumarolic activity had also increased on the SE side of the summit crater.

Figure 118. A new lava dome in the summit crater of Colima on 19 February 2016. Courtesy of CUEIV-UdC (http://www.ucol.mx/enterate/nota.php?docto=2473).

Figure 119. The lava dome at Colima photographed on 29 February 2016 was noticeably larger than when first photographed ten days earlier. Courtesy of SkyAlert (2 March 2016).

Ash plume heights during March 2016 were slightly lower than during February (4.0-6.1 km altitude). Most of the plumes continued to drift NE or SE, and most dissipated within 50 km. During the first week of April, scientists observed fresh ashfall covering the dome at the center of the crater, which had not changed significantly since the previous overflight at the end of February. Persistent ash plumes continued throughout April with a three-minute-long ash emission recorded on 28 April by Colima's webcam.

The frequency of ash emissions decreased during May 2016 and further still during June 2016, when advisories from the Washington VAAC only appeared during five days of the month (1, 4, 13, 23, 30); the plume heights remained similar to previous months, except for a 16 May plume observed moving ENE at 7.6 km. After a two week pause, ash emissions resumed on 17 July with plume heights ranging from 4.3 to 7.3 km altitude through the end of the month. During the second half of August and for part of September, intermittent plumes did not exceed 6.1 km altitude, and dissipated within a few tens of kilometers of the summit.

The Unidad Estatal de Protección Civil de Colima reported that on 26 September seismicity at Colima increased, and incandescence appeared at the crater. On 27 September, small landslides originating from the growing lava dome traveled 100 m down the S flank. By the evening of 30 September, the webcam showed intense activity and crater incandescence as lava spilled over the crater rim and flowed down the SW flank (figure 120). An intense thermal anomaly was visible in short-wave infrared satellite images. An ash plume detected on 1 October in satellite images drifted almost 40 km S and SW; the webcam recorded explosions and pyroclastic flows down the flanks. The OMI instrument on the Aura satellite also recorded significant SO₂ plumes drifting W and SW from Colima on 30 September and 1 October (figure 121).

Figure 120. Intense activity at Colima during the late evening of 30 September 2016 (2014 CST), as a new lava flow emerged from the summit crater and moved down the SW flank. Image from the Webcams de México Colima webcam located at the Laguna de Carrizalillos in Comala, about 25 km SW of the summit.

Figure 121. Sulfur dioxide plumes from Colima were captured by the OMI instrument on the Aura satellite on 30 September (upper) and 1 October 2016 (lower). Colima is on the left (west) side, near the coast. The other SO2 plume in central Mexico on the 1 October is from Popocatépetl. The red pixels indicate Dobson Unit (DU) values greater than 2. DU are a measure of molecular density of SO2 in the atmosphere. Courtesy of NASA Goddard Space Flight Center.

According to news articles (Noticieros Televisa), during 29 September-1 October gas-and-ash plumes rose 4 km and caused ashfall in nearby areas, including La Becererra, La Yerbabuena, San Antonio, and El Jabali in the municipality of Comala (26 km SW), Montitlán in the municipality of Cuauhtémoc (34 km NW), and Juan Barragan in Tonila, Jalisco (14 km SE). On 1 October the Colima State government stated that the communities of La Yerbabuena (80 people) and La Becerrera (230 people) were preemptively evacuated, and an exclusion zone was extended to 12 km on the SW side. A news article noted that Juan Barragan was also evacuated.

The lava flow continued down the flank with incandescent rockfalls (figure 122) and occasional pyroclastic flows; by 4 October it had reached the base of the cone. The volume of the lava dome was estimated to have exceeded 1.2 million cubic meters (figure 123). By 8 October 2016, the lava flow was about 2,000 m long and 270 m wide at its front at the base of the cone. The Washington VAAC reported a strong hotspot consistent with the lava flow in satellite imagery on 9 October. On 13 October, they noted an ash plume that had drifted over 200 km W from the summit. Strong, multi-pixel, daily thermal alerts were issued from MODVOLC during 1-14 October. On 21 October, UEPCC reported that lava continued to flow down the S flank. It was 2.3 km long, 320 m wide, and had an estimated volume of 21 million m³.

Figure 122. A lava flow descends the S flank of Colima on 2 October 2016. Image by Raúl Arámbula, courtesy of Red Sismologica Telemetrica del Estado de Colima-Centro Universitario de Estudios e Investigaciones de Vulcanologia-Universidad de Colima (RESCO-CUEIV-UdeC).

Figure 123. The lava dome overflowing the summit crater at Colima on 5 October 2016. Image by Raúl Arámbula, courtesy of RESCO-CUIEV-UdeC.

Multiple ash plumes rose to altitudes of 5.5-8.2 km and drifted 25-40 km S, SW, and W during 2-4 October. Ashfall was reported in areas on the S and SW flanks. Ash explosions were also frequent throughout the rest of October, with plumes rising to altitudes of 4.3-7 km on many days (figure 124), until they ceased on 4 November for several weeks.

Figure 124. Ash explosion at Colima on 9 October 2016. Steam in the foreground is from the lava flow travelling down the SW flank. Image from the Webcams de México Colima webcam located at the Laguna de Carrizalillos in Comala, about 25 km SW of the summit.

Effusive activity increased again at the very end of October 2016 with the growth of a new lava dome inside the summit crater. By 17 November, a new lava flow was also visible on the S flank (figure 125); it was reported to be about 500 m long by 20 November. After intermittent MODVOLC thermal alerts during late October and early November, they intensified with daily multi-pixel alerts between 15 November and 1 December.

Figure 125. A new lava flow on the S flank of Colima on 17 November 2016. Image from the Webcams de México Colima webcam located at the Laguna de Carrizalillos in Comala, about 25 km SW of the summit.

During 26-28 November 2016, a brief episode of ash emissions sent plumes to 4.9-5.5 km altitude that drifted W, N, and NE as far as 75 km before dissipating. Observations of Colima made on 5 December by UEPCC during a helicopter overflight indicated that the lava flow on the S flank was slowing its advance, and had reached about 1,700 m in length (figure 126).

Figure 126. The lava flow on the S flank of Colima had reached 1.7 km in length on 5 December 2016. Courtesy of UEPCC.

A new series of strong explosions with abundant ash emissions began on 7 December that continued through the end of the month. Multiple daily ash emissions appeared in both the webcam and satellite imagery. The plume on 8 December rose to 7.3 km and extended about 185 km NE of the summit near Lago de Chapala before dissipating. Incandescence during the explosions was visible at night, and glowing blocks were common on the upper flanks.

Ash clouds from multiple emissions were observed drifting W to WSW on 14 December at altitudes from 6.1 to 7.9 km (about 4 km above the summit). These plumes were visible 370 km WSW of the summit the next day. Plumes rose as high as 9.1 km altitude on 15 December, and spread N and NW. A series of strong, multiple daily explosions during 16-18 December included some of the strongest explosions since July 2015 (figure 127). Many of the multiple daily explosions during 19-31 December had plumes rising over 7 km in altitude and drifting over 100 km from the summit before dissipating. MODVOLC thermal alerts appeared on 13 days during December 2016.

Figure 127. A strong explosion at Colima on 18 December 2016. Image from the Webcams de México Colima webcam located at the Laguna de Carrizalillos in Comala, about 25 km SW of the summit.

Frequent strong explosive activity continued during January 2017. For the first three weeks of the month, the multiple daily plumes rose to altitudes of 4.6-7.6 km, drifting in multiple directions, some as far as 135 km. The UEPCC reported that at 0027 on 18 January a moderate-to-large explosion ejected incandescent material as far as 2 km onto the W, SW, SE, and N flanks. Based on webcam and satellite images, the México City MWO, and pilot observations, the Washington VAAC reported that during 18-24 January ash plumes rose to altitudes of 4.1-6.7 km and drifted in multiple directions. On 19 January, strong explosions were recorded by the webcam and noted by the Jalisco Civil Protection Agency (figure 128); they also reported ashfall in Comala and Cuauhtémoc. A strong thermal anomaly was identified in satellite images. Remnant ash clouds from the explosions were centered about 350 km SE on 20 January. A large ash plume rose to an altitude of 10.7 km on 23 January and drifted NE; several plumes that rose to over 7 km altitude were reported through the end of January. MODVOLC thermal alerts were issued on 11 days during January, but no further alerts appeared through June 2017.

Figure 128. Eruption at Colima at 0431 on 19 January 2017. Courtesy of Sergio Tapiro.

The CUEIV-UdC reported that a large explosion at 1732 on 3 February 2017 generated an ash plume that rose 6 km above the crater rim and drifted SSW (figure 129). The Washington VAAC reported the plume at 7.6 km altitude (3.7 km above the crater) shortly before midnight on 4 February. The CUEIV-UdC also noted that a small pyroclastic flow traveled down the E flank. Their report stated that the internal crater was about 250 m in diameter and 50-60 m deep; previous lava domes had been destroyed in late September and mid-November 2016.

Figure 129. An explosion at Colima on 3 February 2017 caused an ash plume that the Universidad de Colima reported as rising to six km above the crater, drifting SSW. A small pyroclastic flow descended the E flank. Image from the Webcams de México Colima webcam located at the Laguna de Carrizalillos in Comala, about 25 km SW of the summit.

A brief period of low-intensity explosions during 10-16 February 2017 generated ash plumes reported by the Washington VAAC at 4-5.2 km altitude. There were no further aviation alerts issued during February. According to CUEIV-UdC, a few low-intensity explosions occurred during 3-16 March. The ash plume on 7 March rose about 2 km above the crater and drifted SW. During an overflight in the middle of March, researchers from CUEIV-UdC noted degassing from small explosion craters on the floor of the main crater; there was no evidence of effusive activity or growth of a new dome. After the middle of March, seismicity steadily decreased; CUEIV-UdC reported landslides every week through June, but no additional ash emissions were reported.

The MIROVA radiative power plot of the MODIS thermal anomaly data clearly shows the thermal activity at Colima during September 2016-February 2017 (figure 130).

Figure 130. MIROVA log radiative power data from MODIS thermal anomaly satellite information clearly shows the strong thermal anomalies from the lava flows at Colima during September 2016-February 2017. The thermal anomalies shown in black after February 2017 are not located on the edifice and are not related to volcanic activity. Courtesy of MIROVA.

Geologic Background. The Colima volcanic complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the 4320 m high point of the complex) on the north and the 3850-m-high historically active Volcán de Colima at the south. A group of cinder cones of late-Pleistocene age is located on the floor of the Colima graben west and east of the Colima complex. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide caldera, breached to the south, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, and have produced a thick apron of debris-avalanche deposits on three sides of the complex. Frequent historical eruptions date back to the 16th century. Occasional major explosive eruptions (most recently in 1913) have destroyed the summit and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth.

Information Contacts: Unidad Estatal de Protección Civil de Colima (UEPCC), Roberto Esperón 1170 Col. de los Trabajadores, C.P. 28020 (URL: http://www.proteccioncivil.col.gob.mx/); Centro Universitario de Estudios e Investigaciones de Vulcanologia (CUEIV-UdC), Universidad de Colima, Colima, Col. 28045, México; Centro Universitario de Estudios Vulcanologicos y Facultad de Ciencias de la Universidad de Colima, Avenida Universidad 333, Colima, Col., 28045 México (URL: http://portal.ucol.mx/cueiv/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Webcams de México (URL: http://www.webcamsdemexico.com/); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/); SkyAlert, Twitter (@SkyAlertMx) (URL: https://twitter.com/SkyAlertMx/status/705188862318882816); Sergio Tapiro, Twitter (@tapirofoto); Noticieros Televisa (URL: http://noticeros.televisa.com).

Following explosions that produced ash plumes in early July 2010 (BGVN 36:07), no additional activity was noted from Ebeko by the Kamchatkan Volcanic Eruption Response Team (KVERT) until October 2016. This rather remote volcano on the N end of Paramushir Island in the Kuril Islands (figure 6) contains many craters, lakes, and thermal features (figure 7). Ash plumes were observed on 20 October 2016 and continued to be detected intermittently through 19 April 2017 (table 4).

Figure 6. Satellite imagery from Google Earth showing the location of Ebeko volcano on the N end of Paramushir Island, Kuril Islands. The village and seaport of Severo-Kurilsk, the largest populated center on the island, is about 7 km E. Courtesy of Google Earth; specific sources of data are shown on the image.

Figure 7. Sketch map showing features in the crater area of Ebeko volcano. (1) thermal fields in pink, (2) fumaroles, (3) pots of thermal water, (4) crater lakes in blue, (5) rims of major craters. Roman numerals denote thermal fields: (I) Active Funnel (in the North Crater), (II) South Crater, (III) West Field, (IV) Northeastern Field, (V) Gremuchaya fumarole field, (VI) Florenskii fumarole field, (VII) First Eastern Field, (VIII) Second Eastern Field, (IX) Southeastern Field, (X) Lagernyi Brook field, (XI) Second Southeastern Field, (XII) Third Southeastern Field. From Rychagov and others, 2010.

Table 4. Summary of activity at Ebeko volcano from mid-October 2016 to mid-April 2017. ACC is Aviation Color Code. Data courtesy of KVERT.

According to observers about 7 km E in the city of Severo-Kurilsk, a gas-and-steam plume containing a small amount of ash rose from Ebeko on 20 October 2016 (figure 8), marking the start of its most recent eruption. The Aviation Color Code (ACC) was raised from Green to Yellow. Later that day observers noted gas, steam, and ash plumes rising from the volcano. Ground-based and satellite observations during 21-23 October indicated quiet conditions; consequently, the ACC was lowered to Green on 24 October.

Figure 8. Ash explosions from Ebeko at 2245 UTC on 19 October 2016 were photographed from Severo-Kurilsk, 7 km E of the volcano. Photo by T. Kotenko; courtesy of Institute of Volcanology and Seismology FEB RAS, KVERT.

On 8-9 December 2016 the ACC was again raised to Yellow when a gas and steam plume containing a small amount of ash was observed. Ash rose from both Sredniy Crater (middle) and Severny Crater (northern) during 9-10 December (figure 9). Further ash plumes were seen during 17-27 December the ACC was raised to Orange. Minor ash was reported during 30 December 2016-6 January 2017, along with gas and steam plumes. An ash plume rose up to 2 km altitude on 19 January (figure 10), and ash fell in Severo-Kurilsk on 30 January. More frequent explosions took place between 24 February and 19 April 2017 (table 4). Simultaneous explosions from two craters was observed on 15 April (figure 11).

Figure 9. Explosive ash eruption from the Ebeko craters at 0116 UTC on 10 December 2016. Photo by L. Kotenko; courtesy of Institute of Volcanology and Seismology FEB RAS, KVERT.

Figure 10. Ash from an explosive eruption of Ebeko on 19 January 2017 rose up to 2 km altitude. Photo by T. Kotenko; courtesy of Institute of Volcanology and Seismology FEB RAS, KVERT.

Figure 11. Explosions at Ebeko generated ash plumes simultaneously from the active Severny (northern) and Sredniy (middle) craters on 15 April 2017. Photo by T. Kotenko; courtesy of Institute of Volcanology and Seismology FEB RAS, KVERT.

Satellite thermal data from MODVOLC showed no thermal alerts for at least the last 10 years, and MIROVA only identified two low-power anomalies in the past year, one in late February 2017 and the other in late March 2017.

Reference: Rychagov S.N., Belousov V.I., Kotenko ?.A., and Kotenko L.V., 2010, Gas-hydrothermal system of the geothermal deposit, Proceedings World Geothermal Congress 2010 Bali, Indonesia, 25-29 April 2010, 4 p.

Geologic Background. The flat-topped summit of the central cone of Ebeko volcano, one of the most active in the Kuril Islands, occupies the northern end of Paramushir Island. Three summit craters located along a SSW-NNE line form Ebeko volcano proper, at the northern end of a complex of five volcanic cones. Blocky lava flows extend west from Ebeko and SE from the neighboring Nezametnyi cone. The eastern part of the southern crater contains strong solfataras and a large boiling spring. The central crater is filled by a lake about 20 m deep whose shores are lined with steaming solfataras; the northern crater lies across a narrow, low barrier from the central crater and contains a small, cold crescentic lake. Historical activity, recorded since the late-18th century, has been restricted to small-to-moderate explosive eruptions from the summit craters. Intense fumarolic activity occurs in the summit craters, on the outer flanks of the cone, and in lateral explosion craters.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

Karymsky volcano on Russia's Kamchatka Peninsula has a lengthy eruptive history based on both radiocarbon data (back to about 6600 BCE) and historical observations (back to 1771). Much of the volcanic cone is surrounded by lava flows less than 200 years old. The most recent activity, consisting of frequent ash explosions and a few lava flows deposited on the flanks, has been ongoing for several decades. The most recent previous report described numerous ash explosions, persistent thermal anomalies, and moderate seismic activity through 2014 (BGVN 40:09). This report covers similar activity from January 2015 through May 2017. Information was compiled from the Kamchatka Volcanic Eruptions Response Team (KVERT), the Tokyo Volcanic Ash Advisory Center (VAAC), and several sources of satellite data.

Ash-bearing explosions and thermal anomalies characterized activity throughout 2015, beginning with an explosion on 19 January. Ash plumes were common through early March 2016, after which only steam-and-gas emissions and occasional thermal anomalies were noted, although fresh ash deposits were observed near the volcano in the second half of March. A brief episode of explosive activity during 5-8 October 2016 produced low-level ash plumes that drifted for hundreds of kilometers. No additional activity was reported through May 2017.

Activity during 2015. An explosive event at Karymsky on 19 January 2015 signaled a return to activity after a few months of quiet. The ash plume from the explosion extended 50 km SE, and the NASA Earth Observatory captured a satellite image showing trace ash deposits from the event trending SE across the snow-covered landscape (figure 34). Ashfall deposits were seen on 1 March (10-15 km E and SE) and 7 March.

Figure 34. A streak of dark ash extends SE from Karymsky's summit amidst a backdrop of snow on 18 January 2015 (UTC). The Operational Land Imager (OLI) aboard the Landsat 8 satellite acquired this natural color satellite image. Courtesy of NASA Earth Observatory.

Throughout the year, KVERT reported multiple thermal anomalies and ash plumes each month (table 8). The Tokyo VAAC issued 192 aviation alerts during the year, and the MODVOLC system reported eight thermal alerts in January, one in July, and two in August. Ash plume altitudes ranged from 2.1 to 7 km. Continuous ash emissions were noted during 16 and 29-30 July. The ash plume observed in satellite data on 17 July was 8 km long and 5 km wide. Volcanologists observed multiple explosions during 21-22 July, and helicopter pilots in the area reported explosions on 28 July that then lasted for several days (figure 35). Large plumes were also noted during December; on 22 December one was 8 km long and 6 km wide, and on 25 December one was 56 km long and 6 km wide. The highest altitude plumes were reported at 7 km drifting N on 16 and 20 November 2015 by the Tokyo VAAC. Ash plumes drifted in various directions, and were observed as far as 250 km before dissipating.

Table 8. Summary by month of ash plumes and thermal anomalies reported for Karymsky during 2015. Details include dates of thermal anomalies and ash plumes, maximum plume altitude in kilometers, distance in kilometers of ash plume drift, and direction of drift. Multiple thermal anomalies on a given date are shown in parentheses- 23(4)-after the date. 'Date: 7/8' means time zone boundaries presented different reported days for Kamchatka time (KST) and Universal Time (UTC). Sources are KVERT and Tokyo VAAC for ash plume data; KVERT and MODVOLC for thermal data.

Figure 35. Ash plume from an explosion at Karymsky on 30 July 2015. Photo by E. Kalacheva, IVS FEB RAS, courtesy of KVERT.

Activity during January 2016-April 2017. Activity was variable at Karymsky during 2016 (table 9). The Tokyo VAAC issued 132 aviation notices. Ash plumes and thermal anomalies were most frequent during January and February, with over twenty instances of each during February. The plume heights during February exceeded 6 km altitude four times, with the highest plume of the year on 20 February at 7.6 km altitude. Near-continuous ash emissions during the last week of February resulted in satellite observations of ash deposits around the volcano at the end of the month and during the first few days of March (figure 36). Activity decreased significantly during March, although KVERT noted fresh ash deposits again during 18-25 March. Except for thermal anomalies noted on 1 and 6 April, only steam-and-gas emissions were reported; KVERT lowered the Aviation Alert Level from Orange to Yellow (on a four-color scale) at the end of the month. From May to July, KVERT reported a thermal anomaly once each month. Steam-and-gas emissions were the only activity reported in August, and on 2 September, they lowered the Alert Level from Yellow to Green.

Table 9. Summary by month of ash plumes and thermal anomalies reported for Karymsky during 2016. Details include dates of thermal anomalies and ash plumes, maximum plume altitude in kilometers, distance in kilometers of ash plume drift, and direction of drift. Sources are KVERT and Tokyo VAAC for ash plume data; KVERT and MODVOLC for thermal data.

Figure 36. Steam plume from Karymsky on 21 February 2016, and abundant fresh ashfall around the volcano from recent ash emissions. Photo by E. Nenasheva, courtesy of KVERT.

After six months of quiet, the Tokyo VAAC reported an ash plume on 5 (UTC)/6 (KST) October at 2.4 km altitude extending SE. Aviation alerts were issued through 8 October 2016. Although residing at a fairly low altitude (2.4 km), the plume observed in satellite imagery during 7-8 October was visible in satellite imagery drifting 390 km E and SE before dissipating. KVERT briefly raised the Alert Level to Yellow and then to Orange on 7 and 8 October, and then back to Yellow on 19 October. Three weak thermal anomalies appeared in October and one in November; KVERT lowered the Alert Level to Green on 25 November. Karymsky remained at Alert Level Green through May 2017 with no further reports issued from KVERT or the Tokyo VAAC.

Geologic Background. Karymsky, the most active volcano of Kamchatka's eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed during the early Holocene. The caldera cuts the south side of the Pleistocene Dvor volcano and is located outside the north margin of the large mid-Pleistocene Polovinka caldera, which contains the smaller Akademia Nauk and Odnoboky calderas. Most seismicity preceding Karymsky eruptions originated beneath Akademia Nauk caldera, located immediately south. The caldera enclosing Karymsky formed about 7600-7700 radiocarbon years ago; construction of the stratovolcano began about 2000 years later. The latest eruptive period began about 500 years ago, following a 2300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been vulcanian or vulcanian-strombolian with moderate explosive activity and occasional lava flows from the summit crater.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences, (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/).

Hawaii's Kilauea volcano continues the long-term eruptive activity that began in 1983 with lava flows from the East Rift Zone (ERZ) and a convecting lava lake inside Halema'uma'u crater. The US Geological Survey's (USGS) Hawaii Volcano Observatory (HVO) has been monitoring and researching the volcano for over a century since its founding in 1912. HVO provided quarterly reports of activity for July-December 2016, which are summarized below.

Summary of July-December 2016 activity. Activity at Kilauea during the second half of 2016 was consistent with long-term trends of summit inflation punctuated by DI (Deflation-Inflation) events and a slowly rising average lava lake level inside Halema?uma?u crater. Two explosive events prompted by rockfalls into the lake sent spatter high enough to reach the Halema?uma?u rim; a small overflow at the crater occurred in October, the first since April-May 2015.

Pu'u 'O'o activity continued with little change except for the steady advance of the episode 61g lava flow towards the coast. The pahoehoe front reached the Emergency Access Road near the coast on 25 July and cascaded slowly over the seacliff into the ocean on 26 July just after midnight. It was the first time since August 2013 that lava from Pu'u 'O'o entered the sea. A growing lava delta of about 10 hectares (25 acres) at the Kamokuna entry was the focus of attention by visitors until most of it collapsed into the sea on 31 December 2016.

Activity at Halema'uma'u. Eruptive activity at Halema'uma'u crater was typical during July-December 2016, with a slightly elevated lake level for the last quarter of the year. The lava lake circulation pattern continued in the usual N-S direction, with occasional shifts due to short-lived spattering in areas other than the normal Southeast sink. The lake level rose and fell in concert with the regular summit DI events. On 7 September, the lake level rose to the level of the old rim prior to the April/May 2015 crater overflow, 8 m below the current rim (figure 267).

Figure 267. Halema'uma'u lava lake at Kilauea on 7 September 2016 at 1842 HST when the surface level was at the level of the old crater rim, 8 m below the current rim. Photo by M. Patrick, courtesy of Hawaii Volcano Observatory (HVO) (Hawaiian Volcano Observatory Quarterly Report for July-September 2016).

The lowest lake level of the period was 55 m below the floor of Halema'uma'u on 6 October; the lake reached its highest level when it overflowed the rim on 15 October. This was the highest lake level since the overflows in late April to early May 2015, and it covered a small area of about 5,000 m² of the Halema'uma'u crater floor. The latest overflows consisted of two small lobes that spilled onto the crater floor on the SE and NW sides of the lake (figure 268).

Figure 268. Aerial photo of Halema'uma'u crater and lava lake at Kilauea, looking south, showing the two areas where the lake overflowed onto the crater floor on 15 October 2016. The first overflow is on the upper-left side of the lake; the later overflow at is at the lower right side. Photo by T. Orr, 3 November 2016, courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for October-December 2016).

The lava lake surface or spatter from the lake was visible intermittently from the Jaggar Overlook on the NW rim of the caldera. During a few of the deflation phases of the DI events, newly exposed juvenile veneer on the crater walls detached and collapsed into the lake. Many of these collapses were too small to notice on the webcams or produce seismic events, but several events were noteworthy.

On 6 August there was a large collapse at the base of the Halema'uma'u crater wall (above the Southeast sink). The collapse produced a large explosive event, along with a composite seismic event, and vigorous spattering. The main explosive deposit blanketed the rim just east of the closed overlook, with tephra forming a continuous layer up to 20 cm thick. Bombs were deposited over an area 220 m wide (along the rim) and up to 90 m beyond the crater rim, with sparse lapilli thrown across the parking lot. HVO monitoring equipment and some of the remaining wooden fencing for the overlook were burned.

A second explosive event occurred on 19 September, also triggered by a collapse of the crater wall above the Southeast sink. Bombs and smaller scoria reached the Halema'uma'u crater rim and ash was deposited across the parking area and road. Large events also occurred on 4 October around 1100, and again at around noon. The first triggered a composite seismic event and spattering when veneer on the E wall fell into the lake, and the other triggered brief spattering when a large sheet of veneer fell from the SW wall. On 19 and 20 October, explosive events were triggered by rockfalls below the overlook (figure 269). The first, at 0745, deposited spatter and ribbon bombs up to 30 cm long on the rim of Halema'uma'u, and produced muted composite seismicity. The 20 October event occurred at 1225, producing a tephra deposit that extended across the road past the parking lot, and generated weak composite seismicity.

Figure 269. Bombs and spatter from Halema'uma'u crater at Kilauea during October and November 2016. Left: the 20 October explosive event from the HMcam (a webcam on the SE rim of the crater) taken at 1226, showing spatter bombarding the overlook, after the collapse of the crater wall below the webcam. Right: a large bomb thrown from the lava lake during the 28 November explosive event. The fluidity of the spatter allowed it to splat upon impact. Photo by M. Patrick, 28 November 2016, courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for October-December 2016).

At 1159 on 28 November, another slice of crater wall below the HMcam (one of two Halema'uma'u webcams) fell and triggered an explosive event that again threw tephra onto the rim. The tephra deposit was sparse and confined to a narrow area 90-100 m wide along the rim between the two webcams on the SE rim. While most of the spatter bombs were less than 30 cm in size, the largest was about 160 cm long. The clasts were relatively fluidal in texture and most splatted upon impact (figure 269). The power and Ethernet cables for one of the webcams were damaged during this event. A similar event occurred on 2 December at 0658, when a large slab from the overlook crater wall directly below one of the webcams collapsed. This also triggered a small explosive event which bombarded the rim with spatter near the two cameras, and produced rare ribbon bombs close to a meter long. Another large veneer collapse occurred on 13 December at about 1355, when a slab fell from the N wall into the lake and triggered spattering.

Activity at Pu'u 'O'o and the East Rift Zone. There were few notable changes at Pu'u 'O'o cone from July through December. Very slight uplift was observed during 2-4 July that may have corresponded to inflationary tilt. The forked lava stream in the vent on the NE spillway was visible on a 15 July overflight. Subsequent overflights found the streams progressively more crusted over, and no lava was visible in the vent on the 19 August overflight. The W pit had a large collapse of its NE rim that was noticed on 1 September. A few meters had shaved off the rim of the pit, making a pile of rubble on the pit floor.

One of the two vents on the NE spillway re-opened at some point during the day on 2 November. Fieldwork on 3 November showed that the W-pit lava pond was 52 m across and 22 m below the pit rim, at an elevation of 848 m. The pond level was at 847 m when seen again on 29 November, with weak spattering at a few places around the pond perimeter.

The new flow (episode 61g), which began from the NE flank of Pu'u 'O'o cone on 24 May 2016, had reached the top of Pulama pali (cliff) on 28 June 2016 (BGVN 41:08, figure 263). It reached the base of the pali on the last day of June, and began to advance quickly across the coastal plain (figure 270). It was initially quite narrow, about 100 m across, possibly because of the flow high advance rate and confining topography in the area, according to HVO. The flow had slowed by 5 July; it was half way across the coastal plain, with the leading tip about 1.7 km from both the base of the pali and the ocean, and 1.6 km from the closest portion of the FEMA evacuation road that runs along the coast.

Figure 270. Episode 61g lava flow at Kilauea leaves the base of Pulama pali headed across the coastal plain on 2 July 2016. Several channelized 'a'a flows are visible coming down the slope. Location is at the eastern boundary of the National Park and western boundary of the Royal Gardens subdivision. Photo by Kirsten Stephens, courtesy of Hawaii Volcano Observatory (HVO) (Hawaiian Volcano Observatory Quarterly Report for July-September 2016).

The flow front continued to advance slowly over the next few weeks and eventually stalled in mid-July. The stalled front was soon overtaken, however, by breakouts that had been steadily advancing downslope behind the front. These breakouts formed a new front that continued to advance rapidly at up to 170 m/day. By 24 July, the flow front had reached to within about 260 m of the FEMA emergency access road. The next day (25 July) at 1520 HST, the 61g flow crossed the FEMA road (figure 271), and at 0112 HST on 26 July lava spilled over the sea cliff and into the water, marking the start of the rapid growth of the Kamokuna ocean entry.

Figure 271. Episode 61g lava flow of Kilauea crosses the FEMA emergency access road. Left: the lava flow on 25 July 2016 at 1616 HST about 30 minutes after it crossed the road in a thin sheet, photo by L. DeSmither. Right: on 5 August (almost two weeks later), in the same general location as the first, note the amount of flow inflation (HVO geologist for scale), photo by M. Patrick. Both images courtesy of Hawaii Volcano Observatory (HVO) (Hawaiian Volcano Observatory Quarterly Report for July-September 2016).

The flow field continued to widen over the next few months, as scattered breakouts crept down the flow (figure 272). One of these breakouts formed a second ocean entry point several hundred meters to the W of the initial entry. Other, smaller breakouts reached the ocean along the stretch of land between the two main entry points, forming short-lived entries (figure 273). Persistent breakouts near the base of the Pulama pali began to build a ramp, making the pali less steep.

Figure 272. A breakout from the episode 61g flow on the coastal plain of Kilauea on 20 September 2016. Burning vegetation on the pali from the recent flow is visible in the background. Photo by Matt Patrick, courtesy of Hawaii Volcano Observatory (HVO) (Hawaiian Volcano Observatory Quarterly Report for July-September 2016).

Figure 273. Lava flows into the sea at Kilauea from one of the entry points along the Kamokuna ocean entry, as viewed from the sea, on 11 September 2016. Photo by Tom Pfeiffer, courtesy of Volcano Discovery.

Numerous small delta collapses on both the E and W deltas were reported during August and September, but the deltas overall continued to grow. By the end of September the E delta was about 5.2 hectares (12.9 acres), and had developed several large coast-parallel cracks that suggested it was becoming unstable (figure 274). Activity at the W delta was always subordinate to that at the E delta and was abandoned in late September, having reached about 2.6 ha in size.

Figure 274. The E lava delta at the Kamokuna ocean entry at Kilauea on 30 September 2016. Top: the E Kamokuna ocean entry and lava delta, showing large cracks parallel to the sea cliff. Photo by T. Orr. Bottom: thermal image of the delta showing heat in the cracks, and hot water plumes extending out from the ocean entry points. Courtesy of Hawaii Volcano Observatory (HVO) (Hawaiian Volcano Observatory Quarterly Report for July-September 2016).

The only surface activity not on the lower half of the flow field (from the top of the pali to the coast) during July-September was a large breakout from the episode 61g vent on the east flank of Pu'u 'O'o cone that started 29 August. The breakout was active for only a few days and died during the first week of September. On 27 September a skylight abruptly opened a few hundred meters inland from the ocean entry, producing a strong glow at night. Very little surface activity was present on the coastal plain near the Kamokuna ocean entry during October-December. A small breakout started about a kilometer upslope from the park rope line on 24 November, and remained active until the evening of 28 November.

However, breakouts did continue near the Pulama pali during October-December, further building up the intermediate-sloped ramp at the base of the pali (figure 275). The first of these started on 1 October and continued until at least 23 October, having extended a short distance beyond the base of the pali. A breakout started near the bottom of the steepest part of the pali during 22-23 November, producing short-lived channelized flows. The breakout remained active until at least 30 November, but was apparently inactive by 6 December.

Figure 275. Episode 61g eruption of Kilauea on 13 November 2016, captured by the Advanced Land Imager (ALI) on NASA's Earth Observing-1 satellite. The lava first reached the ocean on 26 July, and most of the lava delta created at the Kamokuna entry collapsed into the sea on 31 December 2016. The gray areas in the image show lava that has accumulated since 1983. The 2016 active flow started at a vent just east of the Pu'u 'O'o crater. It moved SE and S through lava tubes below the surface. The signature of a recent surface breakout is the lighter gray area at the base of the Pulama pali (cliff). Courtesy of NASA Earth Observatory.

At the episode 61g vent near Pu'u 'O'o cone, a new breakout started between 0830 and 0840 on 21 November 2016. The ground surface over and just upslope from the vent was fractured and uplifted 3-4 m. The breakout consisted of two branches, one of which generally headed S and was short lived, stagnating during the day of 26 November. The other flowed NE and surrounded the nearby Pu?u Halulu cone before turning to the SE. The flow front of this second branch was about 2 km from the vent when mapped on 17 December (figure 276), but continued to advance through the end of the year. In addition to the 21 November breakout, other short-lived breakouts from the episode 61g vent were active during 1-3 December, 11-12 December, and 25-28 December.

Figure 276. Changes to the flow field of the episode 61g flow between 20 September and 25 December 2016. Courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for October-December 2016).

During an overflight on 3 November, HVO found that the W delta, which became inactive in late September, was approximately 2 ha after losing about 0.6 ha to wave erosion. The E delta at the Kamokuna ocean entry remained very active through December, reaching a relatively stable size of around 10 ha, kept in check by frequent small collapses. Large cracks on the delta parallel to the old sea cliff were apparent, and the delta on the seaward side of the cracks appeared to be tilted, indicating instability. The delta was about 9 ha in size in late December.

During mid-afternoon on 31 December 2016, the E delta began to collapse in pieces. Over the course of a few hours, most of the delta had disappeared into the water, leaving about 1 ha as narrow remnant ledges at the base of the sea cliff (figures 277 and 278). In addition to the delta collapse, roughly 1.6 ha of the older, post-1986 sea cliff also fell into the ocean, likely due to undercutting promoted by the delta collapse. This portion of the old sea cliff was partially above the E edge of the delta, but most of it was adjacent to the delta to the east (figure 278), and included part of the National Park viewing area. The sea cliff collapses produced thick, dusty plumes and large waves that splashed back onto the sea cliff, in some instances. In the days that followed, a few more small slices of unstable sea cliff collapsed into the water. The total area that collapsed, including the delta and the older sea cliff, was approximately 10 ha.

Figure 277. Eastern Kamokuna lava delta (episode 61g flow) at Kilauea, before and after the 31 December 2016 collapse. Left: The delta on 14 October when it was about 6 ha (15 acres) in size. Photo by L. DeSmither. Right: After the 31 December collapse, showing remnants of the delta. Photo by M. Patrick on 1 January 2017. Courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for October-December 2016).

Figure 278. Map of the Kamokuna ocean entry at Kilauea as of 3 January 2017, showing areas of collapse, remaining delta, and other features. Courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for October-December 2016).

Thermal anomaly data. Satellite-based thermal anomaly data from the MODIS instrument generates a strong continuous signal from Kilauea that closely follows the distribution of the active lava flows. As the episode 61g flow emerged from Pu'u 'O'o and headed SE, the thermal signature was strong between Pu'u 'O'o and the Pulama pali during the last week of June as recorded by the University of Hawaii's MODVOLC thermal alert system. By mid-August, a few weeks after the flow had reached the sea, the thermal activity extended from the pali to the Kamokuna ocean entry site (figure 279).

Figure 279. Thermal alerts from MODVOLC at Kilauea during late June and August 2016. Pu'u 'O'o is beneath the pixel in the upper left of the top image. Top: Alerts during 26 June-1 July 2016. The Pulama pali shows as the shaded area underneath the leading SE edge of the flow. Bottom: Alerts during 12-19 August 2016. The lava was hottest between the Pulama pali on the N and the new Kamokuna ocean entry at the bottom of the image. Courtesy of HIGP MODVOLC Thermal Alerts System.

New breakouts from the Pulama pali area were recorded as thermal alerts during the second week of November along with the evidence for continued thermal alerts from the Kamokuna delta at the shoreline. At the vent area of episode 61g, near Pu'u 'O'o cone, new breakouts flowed NE of the cone and were captured as thermal alerts during early December (figure 280).

Figure 280. Thermal alerts from MODVOLC at Kilauea during November and December 2016. Top: New breakouts were reported from the Pulama pali area and were visible in the thermal data during 5-11 November along with the thermal alerts from the Kamokuna lava delta at the shoreline. Bottom: Alerts during 10-16 December 2016 show renewed breakout activity at the episode 61g vent near Pu'u 'O'o (upper left of image) as well as continued activity at the Kamokuna ocean entry on the shoreline. Courtesy of HIGP MODVOLC Thermal Alerts System.

Geologic Background. Kilauea, which overlaps the E flank of the massive Mauna Loa shield volcano, has been Hawaii's most active volcano during historical time. Eruptions are prominent in Polynesian legends; written documentation extending back to only 1820 records frequent summit and flank lava flow eruptions that were interspersed with periods of long-term lava lake activity that lasted until 1924 at Halemaumau crater, within the summit caldera. The 3 x 5 km caldera was formed in several stages about 1500 years ago and during the 18th century; eruptions have also originated from the lengthy East and SW rift zones, which extend to the sea on both sides of the volcano. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1100 years old; 70% of the volcano's surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 km2, destroying nearly 200 houses and adding new coastline to the island.

Information Contacts: Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawai'i National Park, HI 96718, USA (URL: https://volcanoes.usgs.gov/observatories/hvo/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/).

The active crater at Costa Rica's Rincón de la Vieja, which contains a 500-m-wide acid lake, has been the site of numerous historic eruptions at this large volcanic complex. Intermittent phreatic explosions since 2011 have dispersed volcanic debris from the crater lake within a few kilometers of the crater rim and into the surrounding streams a number of times. The most recent previous activity included explosions in September and October 2014, and phreatic eruptions on June, August and October 2015 (BGVN 41:01); this report discusses activity during 2016 and through July 2017. Information comes from the Observatorio Vulcanológico Sismológica de Costa Rica-Universidad Nacional (OVSICORI-UNA) and the Observatorio Sismológico y Vulcanológico de Arenal-Miravalles (OSIVAM-ICE). The OVISAM-ICE reports are published through the Red Sismológica Nacional (RSN), the National Seismological Network. Ejected material is described in the original reports in various ways that appear to be interchangeable rather than signifying actual content differences, so those distinctions are not reflected below unless ash was specified.

The first evidence of a new episode of phreatic explosions was noted during a site visit on 15 February 2016. Numerous explosions during March spread material as far as 2 km from the crater rim. After an explosion on 1 May 2016 there were no further reports until 23 May 2017, when a series of intermittent explosions again ejected material onto the N and NW flanks and sent plumes of steam-and-gas as high as 2 km above the crater rim. The last reported explosion was on 5 July 2017.

Activity decreased at the end of 2015 after the phreatic explosions of 16-21 October. The number of seismic events increased again during February and March 2016. OVSICORI-UNA scientists observed the first evidence of a new episode of phreatic explosions during a field visit on 15 February 2016 when they noted deposits about 20 m from the crater rim. By the end of March, the RSN had reported 25 explosions. Three of the largest explosions occurred on 9 February, 9 March, and 18 March. They were characterized by episodes of tremor in pulses that usually lasted about five minutes prior to the phreatic explosion, and then changed to continuous tremor for several hours afterwards.

OSIVAM-ICE scientists reported photographic evidence of deposits from a 2 March explosion that covered a wide area on the N flank of the active crater (figure 22). They visited on 3 March 2016 and noted fresh deposits from the phreatic explosions about 200 m W of the crater rim (figure 23). They also witnessed three explosions during the afternoon, the longest lasting for 65 seconds.

Figure 22. Deposits of material ejected from the crater lake on the N edge of Rincón de la Vieja associated with an eruptive event that occurred on 2 March 2016 at 1747 local time. Photo from Fernando Madrigal's Sensoria site, courtesy of RSN (Resumen de la actividad sísmica y eruptive del volcán Rincón de la Vieja (Costa Rica) 01 de octubre del 2015 al 15 de marzo del 2016).

Figure 23. Deposit of material from the crater lake at Rincón de la Vieja on 3 March 2016, located about 200 m W of the crater rim. Photo by OSIVAM-ICE scientists, courtesy of RSN (Resumen de la actividad sísmica y eruptive del volcán Rincón de la Vieja (Costa Rica) 01 de octubre del 2015 al 15 de marzo del 2016).

Scientists from OVSICORI-UNA conducted additional site visits during 8 and 10-11 March 2016. On 8 March fresh ash was found about 120 m from the crater rim (figure 24), and a temperature of 55°C was measured remotely for the convection cell in the lake. Based on photographs taken by nearby residents, OVSICORI-UNA scientists estimated that the ash and steam plumes produced by the 9 and 10 March explosions rose 700 and 850 m, respectively, above the crater. Local residents reported to The Tico Times that ash fell on the roofs of their homes within an area up to 6 km around the volcano after the explosion on 9 March, mostly in communities N of the crater (Upala and Buenos Aires).

Figure 24. The N rim of the active crater at Rincón de la Vieja on 8 March 2016 is marked with the outline (white dashes) showing the extent of material ejected during recent explosions. The arrow at the top shows the dominant wind direction. Inset on left shows riverbed deposits of recent material on 8 March, and the right inset images show the plumes from the 9 (upper) and 10 (lower) March explosions. Right inset photos by Jorge Viales, courtesy of OVSICORI (Erupciones del volcán Rincón de la Vieja: Observaciones de Campo).

The character of the deposits changed between February and March 2016, according to a report by OVSICORI scientists. The samples collected in February were rich in elemental sulfur, abundant in the crater lake and in the near-surface sediments. Studies of the March samples showed the presence of clasts of altered rocks, hydrothermal minerals, and elemental sulfur as well as 3-10% fresh glass.

During their summit visit on 10 and 11 March 2016, OVSICORI scientists noted a coating of white sediment, up to 5 mm thick in some places, covering the ground and the vegetation in a 400m-wide area to the SSW of the active crater (figure 25). Deposits extended as far as 2 km away, and coated the flanks of both the active crater and the nearby Von Seeback crater (figure 26).

Figure 25. Material from phreatic explosions cover a Copey shrub at Rincón de la Vieja on 10 March 2016. The plant was located 1.5 km SSW from the active crater. Photo by E. Duarte, courtesy of OVSICORI-UNA (Visita al Volcán Rincón de la Vieja: Mapeo de Efecto y Características de Erupciones Freáticas Recientes).

Figure 26. A view to the ESE on 10 March 2016 from the flank of the Von Seeback crater towards the active crater showing the coating of white sediments from the recent phreatic explosions at Rincón de la Vieja. The arrow points roughly NW showing the direction of sediment dispersal. Material was sampled at site 4 (white circle). Photo by E. Duarte, courtesy of OVSICORI-UNA (Visita al Volcán Rincón de la Vieja: Mapeo de Efecto y Características de Erupciones Freáticas Recientes).

A 15 March explosion generated a 700-m-high plume of water vapor and gas, according to an announcement from OVSICORI-UNA. They also reported an explosion on 1 May 2016 detected for 11 minutes by the seismic network. No further reports were made until May 2017.

A small lahar traveled down the N flank of the crater after an explosion on 23 May 2017. Explosions on 11 and 12 June were recorded seismically, but cloudy weather obscured visual observations. The Washington VAAC, however, noted a hotspot in the infrared satellite data on 11 June 2017 about 30 minutes before the explosion was reported. A diffuse steam plume was observed from Dos Rios de Upala rising about 50 m above the summit on 15 June, and a small phreatic explosion was recorded on 18 June 2017. A larger explosion on 23 June sent a plume 1-2 km above the summit, and ejected material to the W and NW onto the upper N flank toward the Von Seebach crater 2 km to the W. Small phreatic explosions on 5 July ejected material that did not rise above the crater rim.

Geologic Background. Rincón de la Vieja, the largest volcano in NW Costa Rica, is a remote volcanic complex in the Guanacaste Range. The volcano consists of an elongated, arcuate NW-SE-trending ridge that was constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the "Colossus of Guanacaste," it has an estimated volume of 130 km3 and contains at least nine major eruptive centers. Activity has migrated to the SE, where the youngest-looking craters are located. The twin cone of 1916-m-high Santa María volcano, the highest peak of the complex, is located at the eastern end of a smaller, 5-km-wide caldera and has a 500-m-wide crater. A plinian eruption producing the 0.25 km3 Río Blanca tephra about 3500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous historical eruptions possibly dating back to the 16th century, have been from the prominent active crater containing a 500-m-wide acid lake located ENE of Von Seebach crater.

Information Contacts: Observatorio Vulcanológico Sismológica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/); Observatorio Sismológico y Vulcanológico Arenal-Miravalles del Instituto Costarricense de Electricidad (OSIVAM-ICE), Sección de Sismología, Vulcanología y Exploración Geofísica, Escuela Centroamericana de Geología, Apdo. 214-2060, San Pedro, Costa Rica (URL: http://rsn.ucr.ac.cr/); The Tico Times (URL: http://www.ticotimes.net/2016/03/10/costa-rica-rincon-de-la-vieja-volcano-vapor-ash-explosions).

Ecuador's Sangay, isolated on the east side of the Andean crest, has exhibited frequent eruptive activity over the last 400 years. Its remoteness has made ground observations difficult until recent times, and thus most information has come from aviation reports from the Washington Volcanic Ash Advisory Center (VAAC) and MODIS (Moderate Resolution Imaging Spectroradiometer) satellite-based data. Thermal anomaly information is reported by the University of Hawaii's MODVOLC system and the Italian MIROVA Volcano HotSpot Detection System. Ecuador's Instituto Geofísico (IG) issues periodic Special Reports of activity. This report summarizes the intermittent nature of the eruptions from 2011-2013, and covers renewed activity during January 2015 through July 2017.

Summary of activity during 2011-2013. Activity during 2011 (figure 14) began with a continuation of the intermittent ash emissions and thermal anomalies that persisted throughout 2010 (BGVN 36:01). Ash plumes during January and February 2011 were reported at typical altitudes between 6 and 8 km; thermal alerts appeared once each during January and March. No activity was reported after 2 March until a new series of thermal alerts began more than 3 months later on 6 June 2011; they were intermittent from then through 19 September 2012, with reports occurring during 1-4 days of all but three months. Ash emissions were also intermittent during this time, with VAAC reports issued during eight of the months from 2 August 2011-28 July 2012 for plumes reported at altitudes of 6-8 km. They also generally occurred during 1-4 days of the month. A four-month break in activity followed until ash plumes were reported on 25 January 2013; they were intermittent until 24 May 2013. MODVOLC thermal anomalies were also reported during this time, on 2 February, 25 March, and 3-4 May.

Figure 14. Summary chart of ash emissions and thermal anomalies reported from Sangay during January 2010 to early August 2017. Red bars show eruptive periods where there are reports of either ash plumes or thermal anomalies without a lack of observed activity for more than 3 months. Rows with pink cells indicate dates with thermal anomalies (MODVOLC or MIROVA). Rows with blue cells indicate dates with ash emissions as reported by the Washington VAAC. A range of dates means that activity occurred at least on those two dates, but may not have been continuous. Data courtesy of Washington VAAC, HIGP MODVOLC Thermal Alerts System, and MIROVA.

Summary of activity during January 2015-July 2017. After 19 months of quiet from June 2013 through December 2014, an ash plume reported on 19 January 2015 marked the beginning of a new eruptive episode that included ash plumes, lava flows, and block avalanches between 19 January and 7 April 2015. The next reported activity included both ash emissions and thermal anomalies observed almost a year later on 25 March 2016, although IG had reported increases in seismicity during the previous two weeks. Ash emissions and thermal anomalies were intermittent through 16 July 2016. There was a single thermal anomaly seen in MIROVA data on about 10 October and a brief ash emission occurred during 16-17 November 2016, after which Sangay was quiet until a new episode started on 20 July 2017 that was ongoing into August.

Activity during January-April 2015. After a 19-month period of no reported activity (since May 2013), ash emissions were again seen beginning on 18 January 2015 when an ash plume rose to 6.4 km altitude and drifted SW. Additional plumes on 25 January and 4 February rose to 7.3 km and 6.7 km, respectively, and drifted less than 20 km SW (figure 15). Ash plumes primarily observed by pilots between 27 February and 16 March were generally not visible in satellite images due to weather clouds. During this episode, MODVOLC thermal alerts were reported on 26 January; 7, 21, 23 and 27 February; 2,4,18, and 27 March; and 1, 3, and 7 April.

Figure 15. Ash emission at Sangay sometime during 19-26 January 2015. The ash plume eventually reached about 2 km above the 5,286-m-high summit crater. Photo by Gustavo Cruz, courtesy of IG (Informe Especial del Volcan Sangay No 1, 16 March 2015).

In a March 2015 report, IG noted that new lava flows and block-avalanche deposits had been emplaced during January and February 2015. The lava flows descended the SE flank about 900 m (figure 16). Two areas of deposits from block avalanches and ashfall extended 2.5 km ESE from the lava front, and 1.5 km down the S flank. According to IG, there were 21 thermal anomalies identified in MIROVA during 31 January-25 February 2015.

Figure 16. Locations of lava flows and block-avalanche deposits at Sangay that were emplaced during January and February 2015. The new lava flows are shown in red. The ash and block-avalanche deposits are shown in stippled yellow/green. Courtesy of IG (Informe Especial del Volcan Sangay No 1, 16 March 2015).

Activity during March-November 2016. IG reported an increase in seismicity on 5 March 2016, after ten months of no reported activity. An explosion signal was followed by harmonic tremor on 9 March, and IG noted that both a thermal anomaly and an emission drifting S were identified in NOAA satellite images. They inferred that increased seismic "explosion" signals on 14 March were indicative of ash-and-gas emissions, although weather clouds prohibited visual confirmation. Ash emissions rising to 6.1 km altitude were first reported by the Guayaquil MWO on 25 March 2016; they noted two more emissions on 27 and 28 March rising to similar altitudes (7.6 and 6.4 km, respectively), but cloudy weather prevented satellite confirmation. Plumes reported on nine days during April rose to similar altitudes (ranging from 5.5-7 km) and extended 18-30 km N or NW from the summit. A series of daily emissions occurred from 30 April-7 May. The emissions included a plume on 2 May that extended 120 km NW, and one on 6 May that rose to 8.2 km altitude and extended approximately 55 km SW before dissipating. Ash-bearing plumes were reported on 10 more days during the rest of May.

Although no more ash plumes were reported until 16 July 2016, MODVOLC thermal alerts were persistent every month beginning on 25 March and lasting through 5 July (see figure 14 above). The MIROVA data for this period also clearly show persistent thermal anomalies (figure 17). A short-lived eruption event during 16-17 November 2016 consisted of an ash emission that rose to 6.1 km altitude and drifted as far as 290 km SE.

Figure 17. Thermal anomaly data from MIROVA for the year ending on 18 January 2017 at Sangay, showing the eruptive episode of March-July 2016, and a brief anomaly on about 10 October 2016; late October-November anomalies are more than 20 kilometers from the summit and unrelated to volcanism. Courtesy of MIROVA.

Activity beginning July 2017. A new eruptive episode began on 20 July 2017, after eight months without major surface activity. Low-energy ash emissions rising to 3 km above the crater, incandescent block avalanches on the ESE flank (figure 18), and a possible new lava flow were reported by IG. The Washington VAAC reported an ash emission on 20 July rising to 8.2 km altitude and drifting about 80 km W. A plume was reported on 1 August by the Guyaquil MWO but obscured by clouds in satellite images, and a plume on 2 August was seen in webcam images (figure 19).

Figure 18. Incandescent blocks roll down the ESE flank of Sangay during the early morning of 1 August 2017. Courtesy of IG (Informe Especial del Volcán Sangay-2017-No 1, 3 August 2017).

Figure 19. Ash emission at Sangay on 2 August 2017, with the plume rising about 400 m above the summit crater drifting SW. Courtesy of IG (Informe Especial del Volcán Sangay-2017-No 1, 3 August 2017).

Geologic Background. The isolated Sangay volcano, located east of the Andean crest, is the southernmost of Ecuador's volcanoes and its most active. The steep-sided, glacier-covered, dominantly andesitic volcano grew within horseshoe-shaped calderas of two previous edifices, which were destroyed by collapse to the east, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. It towers above the tropical jungle on the east side; on the other sides flat plains of ash have been sculpted by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of a historical eruption was in 1628. More or less continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The almost constant activity has caused frequent changes to the morphology of the summit crater complex.

Information Contacts: Instituto Geofísico (IG), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

An eruption at Sheveluch has been ongoing since 1999, and recent activity there was previously described through February 2016 (BGVN 42:03). During March 2016-July 2017, the same type of activity prevailed as before, consisting of lava dome growth, explosions, and pyroclastic flows. The following data comes from Kamchatka Volcanic Eruption Response Team (KVERT) reports. During this period the Aviation Color Code (ACC) remained at Orange (the second highest level on a four-color scale), except for a brief period on 10 December 2016 and brief periods during May-July 2017 when it was Red (highest level).

Activity during March 2016-April 2017. According to KVERT, ongoing activity during March 2016-April 2017 consisted of lava-dome extrusion onto the N flank accompanied by strong fumarolic activity, dome incandescence, ash explosions, and hot avalanches. Satellite images detected an intense daily thermal anomaly over the dome.

On 18 September 2016, a moderate explosion caused dome collapse and 10-km-long pyroclastic flows. Pyroclastic-flow deposits were noted in the Baydarnaya (also spelled Baidarnaya) River valley to the SSW and in the central part of the S flank.

Ash plumes generated by explosions and re-suspended ash usually occurred several times per month, and generally reached altitudes of 4.5-7 km. On 10 December 2016, explosions generated ash plumes observed in satellite images that rose to altitudes of 10-11 km and drifted 910 km NNE. The ACC was raised to Red. By the following day, no further ash emissions were observed, and the ACC was lowered back to Orange. However, explosions continued in December that sent ash plumes as high as 7 km altitude (figure 42). Typical activity continued through the first few months of 2017, including ash explosions sending plumes to as high as 5-6 km altitude (figure 43) that remained visible in satellite imagery 100 km downwind.

Figure 42. Explosions from Sheveluch sent ash up to 7 km altitude at 2314 UTC on 19 December 2016. Photo by Yu. Demyanchuk; courtesy of Institute of Volcanology and Seismology FEB RAS, KVERT.

Figure 43. Typical activity from Sheveluch is evident on 16 April 2017, with an ash plume rising to around 4 km altitude. Photo by Yu. Demyanchuk; courtesy of Institute of Volcanology and Seismology FEB RAS, KVERT.

Activity during May-July 2017. Beginning In May 2017, explosive activity appeared to intensify. Strong explosions on 12 May 2017 generated ash plumes identified in satellite images that rose to altitudes of 9-10 km, spread 70 km wide, and drifted 115 km NW. The ACC was raised to Red. Pyroclastic flows descended the flanks and produced ash plumes that rose 3.5-4 km and drifted NE. A few hours later, satellite images showed a thermal anomaly but no ash emissions, and the ACC was lowered back to Orange.

According to KVERT, after a series of explosions during 13-14 May (figure 44), powerful explosions on 16 May generated ash plumes that rose 8-11 km in altitude, prompting an increase of the ACC to Red. Pyroclastic flows descended the S flank, producing ash plumes that rose 3.5-4 km in altitude (figure 43) and drifted NE; within a few hours, satellite images did not show any ash emissions; the ACC was lowered to Orange.

Figure 44. Ash plumes rise from explosive activity and pyroclastic flows at Sheveluch on 14 May 2017, seen here to an altitude of about 5 km. Photo by Yu. Demyanchuk; courtesy of Institute of Volcanology and Seismology FEB RAS, KVERT.

Additional explosions occurred 18 May. During 23-25 May 2017 powerful explosions generated ash plumes that rose to an altitude of 8 km and drifted 715 km in different directions. On 25 May, at 0830, explosions generated ash plumes that rose to an altitude of 9-10 km and drifted 16 km NE. The ACC was raised briefly to Red. Within the next 90 minutes, the ash plume was identified in satellite images drifting 82 km ENE. Strong steam-and-gas emissions rose from the lava dome. The ACC was lowered back to Orange.

KVERT reported that during the last week of May and first half of June, powerful explosions generated ash plumes that rose 8 km in altitude and drifted 550-1,554 km in various directions. Pyroclastic flows traveled 10 km. Ashfall was reported in Klyuchi Village (50 km SW) on 8 June.

On 15 June, at 0425, powerful explosions generated ash plumes that rose as high as 12 km altitude (figure 45). The ACC was raised to Red, and then back down to Orange by the end of the day. Ash plumes drifted 1,000 km NE and SW during 15-16 June. Ash fell in Klyuchi (50 km SW), Maiskoe, Kozyrevsk (115 km SW), and Atlasovo (160 km SW).

Figure 45. Photo of an ash cloud from Sheveluch generated by a powerful explosion that began at 1625 UTC on 14 June 2017. Photo by A.V. Voznikov; courtesy of the Institute of Volcanology and Seismology FEB RAS, KVERT.

According to KVERT, explosions on 17, 18, and 27 June generated ash plumes that rose as high as 7-10 km altitude and drifted as far as 1,500 km. Explosions on 2 July sent ash plumes to 10-11 km; one plume drifted 1,050 km SW and another drifted 350 km NE. On 23 July, strong explosions generated ash plumes that sailed up to 11-12 km and drifted 1,400 km E. Explosive activity the next day lasted about 8 hours and generated ash plumes that rose 11.5-12 km in altitude and drifted almost 700 km NE and 1,400 km E. Strong pyroclastic flows were also noted. The ACC was raised to Red. Later that day, only steam-and-gas emissions with a small amount of ash was observed, and the ACC was lowered to Orange.

Thermal anomalies. Thermal anomalies based on MODIS satellite instruments analyzed using the MODVOLC algorithm were frequent during the current reporting period. From 1 March to 31 August 2016 thermal anomalies were detected 11-20 days each month. The number of days each month with anomalies was lower during 1 September 2016 to 30 July 2017 (except for October with 13 days), ranging from 3 days in April and May 2017 to 10 days in March. Only one hotspot was recorded in July 2017. The MIROVA system detected numerous hotspots every month during August 2016-July 2017, most of which were about 5 km or less from the summit with very low power signatures.

Figure 46. Thermal anomalies at Sheveluch identified on MODIS data by the MIROVA system (log radiative power) for the year ending 4 August 2017. Courtesy of MIROVA.

Geologic Background. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1300 km3 volcano is one of Kamchatka's largest and most active volcanic structures. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes dot its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large horseshoe-shaped caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. At least 60 large eruptions have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far East Division, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

Abundant ash emissions, Strombolian activity, pyroclastic flows, lahars, and a few lava flows have all been documented at Tungurahua, which lies in the center of Ecuador. Historical observations are recorded back to 1557, and radiocarbon dates are as old as 7750 BCE. Prior to renewed activity in 1999, the last major eruption had occurred during 1916-1918. Since 1999, there have been numerous eruptive episodes, but only a few with breaks in activity longer than three months. Eight distinct episodes of activity occurred from November 2011 through December 2014 that included 10-km-high ash plumes, Strombolian activity, pyroclastic flows, lahars and a lava flow (BGVN 42:05).

Another eruptive episode during April and May 2015 is described below based on information provided by the Observatorio del Volcán Tungurahua (OVT) of the Instituto Geofísico (IG-EPN) of Ecuador, and aviation alerts from the Washington Volcanic Ash Advisory Center (VAAC). Seismic activity increased after a few months of quiet in late February 2015. A new eruptive episode began on 6 April with tremors and ash emissions, which persisted for the next two weeks. Activity tapered off at the end of April. Intermittent ash emissions and ashfall were observed during May. Rainfall led to numerous lahars every month from January through June, many in drainages on the W flank; some were large enough to disrupt travel on local roads.

Activity during January-March 2015. Tungurahua remained quiet during January 2015, although weather conditions prevented visual monitoring for much of the month. Intermittent gas emissions reached 300 m above the crater a few times. Several hundred millimeters of rain during the second week led to numerous lahars on 9 January that descended the Ulba, Vazcún, Juive, Hacienda, Achupashal, Pingullo, Chontapamba, Romero and Rea quebradas (ravines). Most of the lahars consisted of only muddy water, but three carried debris up to 30 cm in diameter in flows several feet wide, moving material at several cubic meters per second (Palmahurco (Juive), Achupashal, and Rea quebradas). During the last week of January, incandescence was noted at the crater on clear nights.

A lahar on 1 February 2015 in the Yuibug sector, reported by an observer in Bilbao, briefly closed the Penipe-Baños road. Clearer weather at the summit in early February revealed weak gas emissions rising to 500 m above the summit crater. IG reported a gradual increase in seismicity beginning on 16 February 2015. They noted an increase in the number of long-period (LP) earthquakes associated with fluid movement near the summit. They also recorded constant inflation since the beginning of January, with an increase in the rate of inflation of the N flank during February. A small explosion was reported on 18 February, but no other surface changes were observed. The Washington VAAC issued a report of a small burst of possible ash and gas seen by the volcano observatory (OVT) mid-day on 24 February at 5.2 km altitude drifting slowly W.

Observatorio del Volcan Tungurahua (OVT) personnel noted steam and gas emissions during 3-5 March 2015 rising 200-500 m above the crater, but no ash was reported. Rainfall led to a lahar on 23 March that carried 30-cm-diameter blocks down the Quebrada de Juive. Seismic activity fluctuated throughout March. After several months of inflation, a sudden change to deflational deformation began on 26 March, as recorded at the RETU station near the summit crater.

Activity during April-June 2015. Moderate amplitude tremors began during the early morning of 6 April 2015; nearby residents reported noises from the volcano starting around 0730 local time, and minor ashfall was reported in Chacauco, Manzano, and Punzupal Alto. Residents of Palitahua reported a gray ash plume drifting W up to 2 km above the crater (figure 81). The seismic events recorded during the following days were all located at depths of 1-6 km, directly under the crater. Ashfall was reported from 6 to 9 April SW and W of the volcano, primarily in the Choglontus sector. On 8 April, ashfall was reported in Manzano, Choglontus, Bilbao, Chacauco, Pillate, and Quero, with accumulation rates of 135-200 grams per square meter per day (g/m²/day). Ashfall increased in Choglontus, reaching 1000 g/m² during 8 and 9 April. Inflation was again observed at the RETU station beginning on 5 April.

Figure 81. Ash-bearing emissions from Tungurahua drift NW on 6 April 2015. Photo by J. Garcia, courtesy of OVT/IG-EPN (Informe No. 789, Síntesis Semanal del Estado del Volcán Tungurahua, del 31 de marzo al 07 de abril del 2015).

The webcam revealed continuous emissions of ash beginning on 6 April 2015. A plume was reported at 6.1 km altitude moving W until the following day. On 8 April OVT reported dense ash emissions to 5.9 km altitude, drifting NW. Weather clouds prevented observation in satellite imagery during these days. Local aircraft indicated ash present at 6.7 km altitude on 9 April in spite of extensive weather clouds. A swarm of "drumbeat" LP earthquakes on 10-11 April was followed by moderate ash emissions on 12 April. On 11 April, IG reported an ash cloud moving W and NW from the summit at 5.5 km altitude. An emission on 14 April with moderate amounts of ash rose 500 m above the summit and drifted WSW (figure 82).

Figure 82. An ash emission rises to 500 m above the summit at Tungurahua on 14 April 2015, and drifts WSW. Photo by B. Bernard, Courtesy of OVT/IG-EPN (Informe No. 791, Síntesis Semanal del Estado del Volcán Tungurahua, del 13 al 21 de abril del 2015).

An explosion on 15 April generated an ash plume that reached 3 km above the summit crater (figure 83). Later in the day ash emissions rose to 2 km above the crater and drifted W. The Washington VAAC reported a continuous ash plume visible in satellite imagery on 15 April moving W from the summit at 6.1 km altitude (1 km above the summit). Although the plume appeared to be almost 100 km long, ashfall reports were limited to areas within 15 km of the summit. Collected ash was mainly composed of dense lithic fragments, euhedral crystals, and oxidized particles, and was not considered juvenile material (from fresh magma). Additional ashfall was reported up through 17 April in Palictahua, El Guanto, El Mirador, El Santuario, Mapayacu, Puela, Chontapamba, and Sabañag.

Figure 83. An ash plume from an explosion at Tungurahua rises 2 km above the summit crater on 15 April 2015. Photo by B. Bernard, Courtesy of OVT/IG-EPN (Informe No. 791, Síntesis Semanal del Estado del Volcán Tungurahua, del 13 al 21 de abril del 2015).

Ash emissions continued at a lower level of frequency and energy after 17 April 2015 (figure 84), and seismic activity notably decreased. There were minor emissions coincident with seismic tremors that produced gray to black fine-grained ashfall mainly to the W of the volcano in Bilbao and Chontapamba through 27 April. Deformation changed from inflation to deflation beginning on 21 April, but after five days, switched back to inflation on 26 April. Plumes with moderate ash content were observed rising to 1 or 2 km above the summit on clear days. An emission on 28 April contained modest amounts of ash and drifted NW.

Figure 84. A double column of steam and red-brown ash rises 500 m above the crater at Tungurahua and drifts W on 17 April 2015. Photo by B. Bernard, Courtesy of OVT/IG-EPN (Informe No. 791, Síntesis Semanal del Estado del Volcán Tungurahua, del 13 al 21 de abril del 2015).

Intense rains occurred on 25 and 26 April 2015 that were large enough to generate significant lahars. On 25 April, lahars were reported in the Chontapamba and Romero ravines moving blocks up to 1 m in diameter. Muddy water was observed in the Achupashal ravine. On 26 April, lahars were reported in the Juive, Mapayacu, Romero, and Chontapamba drainages. Lahars caused a high-frequency seismic signal from the Pondoa ravine during the late morning. The flow rates doubled in Vazcún and Puela ravines, which filled with muddy water. A large lahar was also reported in the Quebrada del Pingullo, and debris was reported in the Clementina, Juive Chico, and La Pampa creeks (figure 85).

Figure 85. Mud and debris filled La Pampa quebrada (ravine) at Tungurahua after heavy rains on 26 April 2015. Photo by S. Aguaiza, courtesy of OVT/IG-EPN (Informe No. 792, Síntesis Semanal del Estado del Volcán Tungurahua, del 21 al 28 de abril del 2015).

During the first week of May 2015, constant steam emissions rose 1 km above the summit crater. The vapor was characterized by very low amounts of ash. On 4 May, ashfall was reported in the Bilbao sector, but not corroborated from other areas. Steam with low to moderate ash content continued through 12 May, with plumes rising 1 km above the summit, mostly drifting W and SW. As a result, ash falls were reported in Manzano, Choglontús, Yuibug and Bilbao. On 10 and 11 May, intense and prolonged rains led to significant lahars in Q. Romero, Ingapirca, Chontapamba, Achupashal, and Ulba, and smaller lahars in several other ravines. Small mudflows and lahars also occurred in the ravines on the W flank on 12, 14, and 15 May. Cloudy weather mostly prevented views of the summit, but continuous steam emissions were observed when it cleared. Fine-grained gray ashfall was reported in Choglontus on 15 and 20 May.

Minor emissions of steam with no ash to 500 m above the crater, drifting mostly W, persisted throughout June. Intermittent rains resulted in minor lahars and mudflows that caused little damage. Lahars descended ravines on the W flank on 16 and 17 June. The summit was cloudy and rainy for much of the month, and seismic activity remained low.

Geologic Background. Tungurahua, a steep-sided andesitic-dacitic stratovolcano that towers more than 3 km above its northern base, is one of Ecuador's most active volcanoes. Three major edifices have been sequentially constructed since the mid-Pleistocene over a basement of metamorphic rocks. Tungurahua II was built within the past 14,000 years following the collapse of the initial edifice. Tungurahua II itself collapsed about 3000 years ago and produced a large debris-avalanche deposit and a horseshoe-shaped caldera open to the west, inside which the modern glacier-capped stratovolcano (Tungurahua III) was constructed. Historical eruptions have all originated from the summit crater, accompanied by strong explosions and sometimes by pyroclastic flows and lava flows that reached populated areas at the volcano's base. Prior to a long-term eruption beginning in 1999 that caused the temporary evacuation of the city of Baños at the foot of the volcano, the last major eruption had occurred from 1916 to 1918, although minor activity continued until 1925.

Information Contacts: Instituto Geofísico (IG), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/, archive at: http://www.ssd.noaa.gov/VAAC/archive.html).

In discussing the week ending on 12 September, "Earthweek" (Newman, 1997) incorrectly claimed that a volcano named "Mount Pinukis" had erupted. Widely read in the US, the dramatic Earthweek report described terrified farmers and a black mushroom cloud that resembled a nuclear explosion. The mountain's location was given as "200 km E of Zamboanga City," a spot well into the sea. The purported eruption had received mention in a Manila Bulletin newspaper report nine days earlier, on 4 September. Their comparatively understated report said that a local police director had disclosed that residents had seen a dormant volcano showing signs of activity.

In response to these news reports Emmanuel Ramos of the Philippine Institute of Volcanology and Seismology (PHIVOLCS) sent a reply on 17 September. PHIVOLCS staff had initially heard that there were some 12 alleged families who fled the mountain and sought shelter in the lowlands. A PHIVOLCS investigation team later found that the reported "families" were actually individuals seeking respite from some politically motivated harassment. The story seems to have stemmed from a local gold rush and an influential politician who wanted to use volcanism as a ploy to exclude residents. PHIVOLCS concluded that no volcanic activity had occurred. They also added that this finding disappointed local politicians but was much welcomed by the residents.

PHIVOLCS spelled the mountain's name as "Pinokis" and from their report it seems that it might be an inactive volcano. There is no known Holocene volcano with a similar name (Simkin and Siebert, 1994). No similar names (Pinokis, Pinukis, Pinakis, etc.) were found listed in the National Imagery and Mapping Agency GEOnet Names Server (http://geonames.nga.mil/gns/html/index.html), a searchable database of 3.3 million non-US geographic-feature names.

The Manila Bulletin report suggested that Pinokis resides on the Zamboanga Peninsula. The Peninsula lies on Mindanao Island's extreme W side where it bounds the Moro Gulf, an arm of the Celebes Sea. The mountainous Peninsula trends NNE-SSW and contains peaks with summit elevations near 1,300 m. Zamboanga City sits at the extreme end of the Peninsula and operates both a major seaport and an international airport.

[Later investigation found that Mt. Pinokis is located in the Lison Valley on the Zamboanga Peninsula, about 170 km NE of Zamboanga City and 30 km NW of Pagadian City. It is adjacent to the two peaks of the Susong Dalaga (Maiden's Breast) and near Mt. Sugarloaf.]

References. Newman, S., 1997, Earthweek, a diary of the planet (week ending 12 September): syndicated newspaper column (URL: http://www.earthweek.com/).

Manila Bulletin, 4 Sept. 1997, Dante's Peak (URL: http://www.mb.com.ph/).

Simkin, T., and Siebert, L., 1994, Volcanoes of the world, 2nd edition: Geoscience Press in association with the Smithsonian Institution Global Volcanism Program, Tucson AZ, 368 p.

Information Contacts: Emmanuel G. Ramos, Deputy Director, Philippine Institute of Volcanology and Seismology, Department of Science and Technology, PHIVOLCS Building, C. P. Garcia Ave., University of the Philippines, Diliman campus, Quezon City, Philippines.

Xinhua News Agency filed a news report on 27 February under the headline "Volcano erupts in Somalia" but the veracity of the story now appears doubtful. The report disclosed the volcano's location as on the W side of the Gedo region, an area along the Ethiopian border just NE of Kenya. The report had relied on the commissioner of the town of Bohol Garas (a settlement described as 40 km NE of the main Al-Itihad headquarters of Luq town) and some or all of the information was relayed by journalists through VHF radio. The report claimed the disaster "wounded six herdsmen" and "claimed the lives of 290 goats grazing near the mountain when the incident took place." Further descriptions included such statements as "the volcano which erupted two days ago [25 February] has melted down the rocks and sand and spread . . . ."

Giday WoldeGabriel returned from three weeks of geological fieldwork in SW Ethiopia, near the Kenyan border, on 25 August. During his time there he inquired of many people, including geologists, if they had heard of a Somalian eruption in the Gedo area; no one had heard of the event. WoldeGabriel stated that he felt the news report could have described an old mine or bomb exploding. Heavy fighting took place in the Gedo region during the Ethio-Somalian war of 1977. Somalia lacks an embassy in Washington DC; when asked during late August, Ayalaw Yiman, an Ethiopian embassy staff member in Washington DC also lacked any knowledge of a Somalian eruption.

A Somalian eruption would be significant since the closest known Holocene volcanoes occur in the central Ethiopian segment of the East African rift system S of Addis Ababa, ~500 km NW of the Gedo area. These Ethiopian rift volcanoes include volcanic fields, shield volcanoes, cinder cones, and stratovolcanoes.

Information Contacts: Xinhua News Agency, 5 Sharp Street West, Wanchai, Hong Kong; Giday WoldeGabriel, EES-1/MS D462, Geology-Geochemistry Group, Los Alamos National Laboratory, Los Alamos, NM 87545; Ayalaw Yiman, Ethiopian Embassy, 2134 Kalorama Rd. NW, Washington DC 20008.

Following the Ms 7.8 earthquake in Turkey on 17 August (BGVN 24:08) an Email message originating in Turkey was circulated, claiming that volcanic activity was observed coincident with the earthquake and suggesting a new (magmatic) volcano in the Sea of Marmara. For reasons outlined below, and in the absence of further evidence, editors of the Bulletin consider this a false report.

The report stated that fishermen near the village of Cinarcik, at the E end of the Sea of Marmara "saw the sea turned red with fireballs" shortly after the onset of the earthquake. They later found dead fish that appeared "fried." Their nets were "burned" while under water and contained samples of rocks alleged to look "magmatic."

No samples of the fish were preserved. A tectonic scientist in Istanbul speculated that hot water released by the earthquake from the many hot springs along the coast in that area may have killed some fish (although they would be boiled rather than fried).

The phenomenon called earthquake lights could explain the "fireballs" reportedly seen by the fishermen. Such effects have been reasonably established associated with large earthquakes, although their origin remains poorly understood. In addition to deformation-triggered piezoelectric effects, earthquake lights have sometimes been explained as due to the release of methane gas in areas of mass wasting (even under water). Omlin and others (1999), for example, found gas hydrate and methane releases associated with mud volcanoes in coastal submarine environments.

The astronomer and author Thomas Gold (Gold, 1998) has a website (Gold, 2000) where he presents a series of alleged quotes from witnesses of earthquakes. We include three such quotes here (along with Gold's dates, attributions, and other comments):

(A) Lima, 30 March 1828. "Water in the bay 'hissed as if hot iron was immersed in it,' bubbles and dead fish rose to the surface, and the anchor chain of HMS Volage was partially fused while lying in the mud on the bottom." (Attributed to Bagnold, 1829; the anchor chain is reported to be on display in the London Navy Museum.)

(B) Romania, 10 November 1940. ". . . a thick layer like a translucid gas above the surface of the soil . . . irregular gas fires . . . flames in rhythm with the movements of the soil . . . flashes like lightning from the floor to the summit of Mt Tampa . . . flames issuing from rocks, which crumbled, with flashes also issuing from non-wooded mountainsides." (Phrases used in eyewitness accounts collected by Demetrescu and Petrescu, 1941).

(C) Sungpan-Pingwu (China), 16, 22, and 23 August 1976. "From March of 1976, various large anomalies were observed over a broad region. . . . At the Wanchia commune of Chungching County, outbursts of natural gas from rock fissures ignited and were difficult to extinguish even by dumping dirt over the fissures. . . . Chu Chieh Cho, of the Provincial Seismological Bureau, related personally seeing a fireball 75 km from the epicenter on the night of 21 July while in the company of three professional seismologists."

Yalciner and others (1999) made a study of coastal areas along the Sea of Marmara after the Izmet earthquake. They found evidence for one or more tsunamis with maximum runups of 2.0-2.5 m. Preliminary modeling of the earthquake's response failed to reproduce the observed runups; the areas of maximum runup instead appeared to correspond most closely with several local mass-failure events. This observation together with the magnitude of the earthquake, and bottom soundings from marine geophysical teams, suggested mass wasting may have been fairly common on the floor of the Sea of Marmara.

Despite a wide range of poorly understood, dramatic processes associated with earthquakes (Izmet 1999 apparently included), there remains little evidence for volcanism around the time of the earthquake. The nearest Holocene volcano lies ~200 km SW of the report location. Neither Turkish geologists nor scientists from other countries in Turkey to study the 17 August earthquake reported any volcanism. The report said the fisherman found "magmatic" rocks; it is unlikely they would be familiar with this term.

The motivation and credibility of the report's originator, Erol Erkmen, are unknown. Certainly, the difficulty in translating from Turkish to English may have caused some problems in understanding. Erkmen is associated with a website devoted to reporting UFO activity in Turkey. Photographs of a "magmatic rock" sample were sent to the Bulletin, but they only showed dark rocks photographed devoid of a scale on a featureless background. The rocks shown did not appear to be vesicular or glassy. What was most significant to Bulletin editors was the report author's progressive reluctance to provide samples or encourage follow-up investigation with local scientists. Without the collaboration of trained scientists on the scene this report cannot be validated.

References. Omlin, A, Damm, E., Mienert, J., and Lukas, D., 1999, In-situ detection of methane releases adjacent to gas hydrate fields on the Norwegian margin: (Abstract) Fall AGU meeting 1999, Eos, American Geophysical Union.

Yalciner, A.C., Borrero, J., Kukano, U., Watts, P., Synolakis, C. E., and Imamura, F., 1999, Field survey of 1999 Izmit tsunami and modeling effort of new tsunami generation mechanism: (Abstract) Fall AGU meeting 1999, Eos, American Geophysical Union.

Gold, T., 1998, The deep hot biosphere: Springer Verlag, 256 p., ISBN: 0387985468.

Gold, T., 2000, Eye-witness accounts of several major earthquakes (URL: http://www.people.cornell.edu/ pages/tg21/eyewit.html).

Information Contacts: Erol Erkmen, Tuvpo Project Alp.

In December 2002 information appeared in Mongolian and Russian newspapers and on national TV that a volcano in Central Mongolia, the Har-Togoo volcano, was producing white vapors and constant acoustic noise. Because of the potential hazard posed to two nearby settlements, mainly with regard to potential blocking of rivers, the Director of the Research Center of Astronomy and Geophysics of the Mongolian Academy of Sciences, Dr. Bekhtur, organized a scientific expedition to the volcano on 19-20 March 2003. The scientific team also included M. Ulziibat, seismologist from the same Research Center, M. Ganzorig, the Director of the Institute of Informatics, and A. Ivanov from the Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences.

Geological setting. The Miocene Har-Togoo shield volcano is situated on top of a vast volcanic plateau (figure 1). The 5,000-year-old Khorog (Horog) cone in the Taryatu-Chulutu volcanic field is located 135 km SW and the Quaternary Urun-Dush cone in the Khanuy Gol (Hanuy Gol) volcanic field is 95 km ENE. Pliocene and Quaternary volcanic rocks are also abundant in the vicinity of the Holocene volcanoes (Devyatkin and Smelov, 1979; Logatchev and others, 1982). Analysis of seismic activity recorded by a network of seismic stations across Mongolia shows that earthquakes of magnitude 2-3.5 are scattered around the Har-Togoo volcano at a distance of 10-15 km.

Figure 1. Photograph of the Har-Togoo volcano viewed from west, March 2003. Courtesy of Alexei Ivanov.

Observations during March 2003. The name of the volcano in the Mongolian language means "black-pot" and through questioning of the local inhabitants, it was learned that there is a local myth that a dragon lived in the volcano. The local inhabitants also mentioned that marmots, previously abundant in the area, began to migrate westwards five years ago; they are now practically absent from the area.

Acoustic noise and venting of colorless warm gas from a small hole near the summit were noticed in October 2002 by local residents. In December 2002, while snow lay on the ground, the hole was clearly visible to local visitors, and a second hole could be seen a few meters away; it is unclear whether or not white vapors were noticed on this occasion. During the inspection in March 2003 a third hole was seen. The second hole is located within a 3 x 3 m outcrop of cinder and pumice (figure 2) whereas the first and the third holes are located within massive basalts. When close to the holes, constant noise resembled a rapid river heard from afar. The second hole was covered with plastic sheeting fixed at the margins, but the plastic was blown off within 2-3 seconds. Gas from the second hole was sampled in a mechanically pumped glass sampler. Analysis by gas chromatography, performed a week later at the Institute of the Earth's Crust, showed that nitrogen and atmospheric air were the major constituents.

Figure 2. Photograph of the second hole sampled at Har-Togoo, with hammer for scale, March 2003. Courtesy of Alexei Ivanov.

The temperature of the gas at the first, second, and third holes was +1.1, +1.4, and +2.7°C, respectively, while air temperature was -4.6 to -4.7°C (measured on 19 March 2003). Repeated measurements of the temperatures on the next day gave values of +1.1, +0.8, and -6.0°C at the first, second, and third holes, respectively. Air temperature was -9.4°C. To avoid bias due to direct heating from sunlight the measurements were performed under shadow. All measurements were done with Chechtemp2 digital thermometer with precision of ± 0.1°C and accuracy ± 0.3°C.

Inside the mouth of the first hole was 4-10-cm-thick ice with suspended gas bubbles (figure 5). The ice and snow were sampled in plastic bottles, melted, and tested for pH and Eh with digital meters. The pH-meter was calibrated by Horiba Ltd (Kyoto, Japan) standard solutions 4 and 7. Water from melted ice appeared to be slightly acidic (pH 6.52) in comparison to water of melted snow (pH 7.04). Both pH values were within neutral solution values. No prominent difference in Eh (108 and 117 for ice and snow, respectively) was revealed.

Two digital short-period three-component stations were installed on top of Har-Togoo, one 50 m from the degassing holes and one in a remote area on basement rocks, for monitoring during 19-20 March 2003. Every hour 1-3 microseismic events with magnitude <2 were recorded. All seismic events were virtually identical and resembled A-type volcano-tectonic earthquakes (figure 6). Arrival difference between S and P waves were around 0.06-0.3 seconds for the Har-Togoo station and 0.1-1.5 seconds for the remote station. Assuming that the Har-Togoo station was located in the epicentral zone, the events were located at ~1-3 km depth. Seismic episodes similar to volcanic tremors were also recorded (figure 3).

Figure 3. Examples of an A-type volcano-tectonic earthquake and volcanic tremor episodes recorded at the Har-Togoo station on 19 March 2003. Courtesy of Alexei Ivanov.

Conclusions. The abnormal thermal and seismic activities could be the result of either hydrothermal or volcanic processes. This activity could have started in the fall of 2002 when they were directly observed for the first time, or possibly up to five years earlier when marmots started migrating from the area. Further studies are planned to investigate the cause of the fumarolic and seismic activities.

At the end of a second visit in early July, gas venting had stopped, but seismicity was continuing. In August there will be a workshop on Russian-Mongolian cooperation between Institutions of the Russian and Mongolian Academies of Sciences (held in Ulan-Bator, Mongolia), where the work being done on this volcano will be presented.

References. Devyatkin, E.V. and Smelov, S.B., 1979, Position of basalts in sequence of Cenozoic sediments of Mongolia: Izvestiya USSR Academy of Sciences, geological series, no. 1, p. 16-29. (In Russian).

Logatchev, N.A., Devyatkin, E.V., Malaeva, E.M., and others, 1982, Cenozoic deposits of Taryat basin and Chulutu river valley (Central Hangai): Izvestiya USSR Academy of Sciences, geological series, no. 8, p. 76-86. (In Russian).

Geologic Background. The Miocene Har-Togoo shield volcano, also known as Togoo Tologoy, is situated on top of a vast volcanic plateau. The 5,000-year-old Khorog (Horog) cone in the Taryatu-Chulutu volcanic field is located 135 km SW and the Quaternary Urun-Dush cone in the Khanuy Gol (Hanuy Gol) volcanic field is 95 km ENE. Analysis of seismic activity recorded by a network of seismic stations across Mongolia shows that earthquakes of magnitude 2-3.5 are scattered around the Har-Togoo volcano at a distance of 10-15 km.

Information Contacts: Alexei V. Ivanov, Institute of the Earth Crust SB, Russian Academy of Sciences, Irkutsk, Russia; Bekhtur andM. Ulziibat, Research Center of Astronomy and Geophysics, Mongolian Academy of Sciences, Ulan-Bator, Mongolia; M. Ganzorig, Institute of Informatics MAS, Ulan-Bator, Mongolia.

An eruption at Mount Elgon was mistakenly inferred when fumes escaped from this otherwise quiet volcano. The fumes were eventually traced to dung burning in a lava-tube cave. The cave is home to, or visited by, wildlife ranging from bats to elephants. Mt. Elgon (Ol Doinyo Ilgoon) is a stratovolcano on the SW margin of a 13 x 16 km caldera that straddles the Uganda-Kenya border 140 km NE of the N shore of Lake Victoria. No eruptions are known in the historical record or in the Holocene.

On 7 September 2004 the web site of the Kenyan newspaper The Daily Nation reported that villagers sighted and smelled noxious fumes from a cave on the flank of Mt. Elgon during August 2005. The villagers' concerns were taken quite seriously by both nations, to the extent that evacuation of nearby villages was considered.

The Daily Nation article added that shortly after the villagers' reports, Moses Masibo, Kenya's Western Province geology officer visited the cave, confirmed the villagers observations, and added that the temperature in the cave was 170°C. He recommended that nearby villagers move to safer locations. Masibo and Silas Simiyu of KenGens geothermal department collected ashes from the cave for testing.

Gerald Ernst reported on 19 September 2004 that he spoke with two local geologists involved with the Elgon crisis from the Geology Department of the University of Nairobi (Jiromo campus): Professor Nyambok and Zacharia Kuria (the former is a senior scientist who was unable to go in the field; the latter is a junior scientist who visited the site). According to Ernst their interpretation is that somebody set fire to bat guano in one of the caves. The fire was intense and probably explains the vigorous fuming, high temperatures, and suffocated animals. The event was also accompanied by emissions of gases with an ammonia odor. Ernst noted that this was not surprising considering the high nitrogen content of guano—ammonia is highly toxic and can also explain the animal deaths. The intense fumes initially caused substantial panic in the area.

It was Ernst's understanding that the authorities ordered evacuations while awaiting a report from local scientists, but that people returned before the report reached the authorities. The fire presumably prompted the response of local authorities who then urged the University geologists to analyze the situation. By the time geologists arrived, the fuming had ceased, or nearly so. The residue left by the fire and other observations led them to conclude that nothing remotely related to a volcanic eruption had occurred.

However, the incident emphasized the problem due to lack of a seismic station to monitor tectonic activity related to a local triple junction associated with the rift valley or volcanic seismicity. In response, one seismic station was moved from S Kenya to the area of Mt. Elgon so that local seismicity can be monitored in the future.

Information Contacts: Gerald Ernst, Univ. of Ghent, Krijgslaan 281/S8, B-9000, Belgium; Chris Newhall, USGS, Univ. of Washington, Dept. of Earth & Space Sciences, Box 351310, Seattle, WA 98195-1310, USA; The Daily Nation (URL: http://www.nationmedia.com/dailynation/); Uganda Tourist Board (URL: http://www.visituganda.com/).